Hydrostatic Transaxle

ABSTRACT

A hydrostatic transaxle is provided for a vehicle having a first axle and a second axle. The hydrostatic transaxle comprises: a hydraulic pump; a first hydraulic motor drivingly connected to the first axle; a closed circuit fluidly connecting the hydraulic pump to the first hydraulic motor; and a fluid-supply switching device shifted between a supply position for supplying fluid from the closed fluid circuit to a second hydraulic motor, which is disposed on the outside of the hydraulic transaxle and is drivingly connected to the second axle, and a supply-stop position for stopping the supply of fluid from the closed fluid circuit to the second hydraulic motor. The first hydraulic motor is variable in displacement, and the hydrostatic transaxle further comprises a linkage system for associating the switching of the fluid-supply switching device between the supply position and the supply-stop position with operation for changing the displacement of the first hydraulic motor.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a hydrostatic transaxle for a vehiclehaving first and second axles, the hydrostatic transaxle comprising: ahydraulic pump; a hydraulic motor drivingly connected to the first axle;and a closed circuit fluidly connecting the hydraulic pump to thehydraulic motor, wherein a second hydraulic motor, which is disposed onthe outside of the hydrostatic transaxle and drivingly connected to thesecond axle, can receive power from the hydrostatic transaxle.

2. Related Art

Conventionally, as disclosed in JP 2002-87086 A, there is a well-knownfour-wheel drive vehicle equipped with a hydrostatic transaxle. Thevehicle is provided with a first axle (one of front and rear axles)drivingly connected to a hydraulic motor incorporated in the hydrostatictransaxle. The vehicle is also provided with a second axle (the other offront and rear axles), which is drivingly connected to an output portionof the hydraulic motor through a mechanical transmission linkageincluding a propeller shaft and a mechanical drive-mode change clutchthat is shiftable between a clutch-on position for establishing afour-wheel drive mode and a clutch-off position for establishing atwo-wheel drive mode.

Such a conventional hydrostatic transaxle may be provided with asub-transmission, such as a gear train or a belt transmission, disposedon the downstream of the hydraulic motor. However, the switching of themechanical clutch accelerates abrasion of components of thesub-transmission, and causes noise and shock.

An alternative conventional vehicle equipped with the above-mentionedhydrostatic transaxle is provided with a second hydraulic motor disposedon the outside of the hydrostatic transaxle so as to drive the secondaxle, and a fluid passage including at least one pipe is interposedbetween the hydrostatic transaxle and the second hydraulic motor. Inthis state, a hydraulic switching valve serving as a drive-mode changevalve, which is shiftable between a supply position for supplying fluidto the second hydraulic motor, i.e., for the four-wheel drive mode, anda supply-stop position for stopping the fluid supply to the secondhydraulic motor, i.e., for the two-wheel drive mode, has to be disposedon the fluid passage.

Here, the drive-mode change valve is desired to have no exposed fluidpipe such as to complicate the assembling of the hydrostatic transaxleand to reduce efficiency of manufacture of the vehicle. Further, thedrive-mode of the vehicle is desired to be automatically changedaccording to the sub-speed change operation for changing the speed stageof the sub-transmission without requiring the vehicle to be stopped forthe drive-mode change operation.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a hydrostatic transaxleadapted for a vehicle having first and second axles, the hydrostatictransaxle comprising: a hydraulic pump; a first hydraulic motordrivingly connected to a first axle; and a closed fluid circuit fluidlyconnecting the hydraulic pump to the first hydraulic motor, wherein thehydrostatic transaxle is convenient for supplying fluid to a secondhydraulic motor, which is disposed outward from the hydrostatictransaxle and is drivingly connected to a second axle.

To achieve the object, according to the invention, a hydrostatictransaxle for a vehicle having a first axle and a second axle,comprises: a hydraulic pump; a first hydraulic motor drivingly connectedto the first axle; and a closed circuit fluidly connecting the hydraulicpump to the first hydraulic motor. The hydrostatic transaxle ischaracterized in that it further comprises a fluid-supply switchingdevice shifted between a supply position for supplying fluid from theclosed fluid circuit to a second hydraulic motor, which is disposed onthe outside of the hydraulic transaxle and is drivingly connected to thesecond axle, and a supply-stop position for stopping the supply of fluidfrom the closed fluid circuit to the second hydraulic motor.

Since the hydrostatic transaxle comprises the fluid-supply switchingdevice, the hydrostatic transaxle requires no additional fluid supplydevice such as an exposed fluid pipe to be extended therefrom to thefluid-supply switching device, thereby reducing the number of parts andcosts, and simplifying the assembling of the hydrostatic transaxle andimproving the manufacture efficiency of the vehicle.

Preferably, the first hydraulic motor is variable in displacement, andthe hydrostatic transaxle further comprises a linkage system forassociating the switching of the fluid-supply switching device betweenthe supply position and the supply-stop position with operation forchanging the displacement of the first hydraulic motor.

Therefore, the fluid-supply switching device is automatically switchedaccording to the operation for changing the displacement of the firsthydraulic motor. In other words, the vehicle can travel in an optimaldrive mode (either a two-wheel drive mode or a four-wheel drive mode)automatically selected correspondingly to the speed-stage of thehydrostatic transaxle established by the selected displacement of thefirst hydraulic motor.

Preferably, at least either a small displacement or a large displacementof the first hydraulic motor is selected. The linkage system sets thefluid-supply switching device to the supply position when the largedisplacement of the first hydraulic motor is selected. The linkagesystem sets the fluid-supply switching device to the supply-stopposition when the small displacement of the first hydraulic motor isselected.

Therefore, when the vehicle travels at work or on a rough road or climbsa steep slope, the large displacement of the first hydraulic motor isselected so as to ensure slow and high-torque rotation of the firstaxle, and the linkage system automatically sets the fluid-supplyswitching device to the supply position so as to transmit the rotationforce to the second axle, thereby ensuring smooth traveling of thevehicle. When the vehicle normally travels, the small displacement ofthe first hydraulic motor is selected so as to ensure efficienthigh-speed rotation of the first axle, and the linkage systemautomatically sets the fluid-supply switching device to the supply-stopposition so as to isolate the second axle from the rotation force of thefirst hydraulic motor, thereby ensuring efficient fuel consumption andsmooth turning of the vehicle.

Further preferably, the first hydraulic motor is provide with a rotaryshaft for changing the displacement of the first hydraulic motor, andwherein the fluid-supply switching device is a rotary valve having arotary axis disposed in parallel to the rotary shaft of the firsthydraulic motor.

Therefore, the space between the rotary shaft of the first hydraulicmotor and the rotary valve serving as the fluid-supply switching deviceis minimized, and the linkage system is compactly disposed in this spaceso as to minimize the hydrostatic transaxle.

Further preferably, the hydrostatic transaxle further comprises: adisplacement control device for changing the displacement of the firsthydraulic motor; and a cushion mechanism. The displacement controldevice has a movable range between at least two positions (in the casethat at least either the large displacement or the small displacement ofthe first hydraulic motor is selected, the at least two positions are alarge displacement position for establishing the large displacement ofthe first hydraulic motor, and a small displacement position forestablishing the small displacement of the second hydraulic motor). Thecushion mechanism is provided in the linkage system so as to make thetwo positions of the displacement control device in the movable rangecorrespond to the supply and supply-stop positions of the fluid-supplyswitching device, respectively, (to make the large displacement positionof the displacement control device correspond to the supply position andto make the small displacement position of the displacement controldevice correspond to the supply-stop position,) even when the movablerange of the displacement control device is different from the shiftablerange of the fluid-supply switching device between the supply positionand the supply-stop position.

Therefore, the cushion mechanism ensures the association of the shift ofthe fluid-supply switching device between the supply position and thesupply-stop position with the operation of the displacement controldevice for changing the displacement of the first hydraulic motor, evenif the movable range of the displacement control device is smaller orlarger than the shiftable range of the fluid-supply switching device.

Further preferably, the linkage system includes a link elementinterposed between the displacement control device and the fluid-supplyswitching device so as to serve as the cushion mechanism. A link ratiobetween the displacement control device and the link element isdifferent from a link ratio between the fluid-supply switching deviceand the link element, so as to correspond to the difference between themovable range of the displacement control device and the shiftable rangeof the fluid-supply switching device.

Therefore, while various vehicles require various differences betweenthe movable range of the displacement control device and the shiftablerange of the fluid-supply switching device, only the link element isoptionally designed so as to correspond to the difference between themovable range of the displacement control device and the shiftable rangeof the fluid-supply switching device in a target vehicle, whereby thelinkage system having the cushion mechanism, i.e., the linkage system,which surely associates the shift of the fluid-supply switching devicebetween the supply position and the supply-stop position with theoperation of the displacement control device for changing thedisplacement of the first hydraulic motor, can be easily adapted for anyvehicle.

Alternatively preferably, the linkage system includes an elastic elementserving as the cushion mechanism interposed between the displacementcontrol device and the fluid-supply switching device so as to allowmovement of one of the displacement control device and the fluid-supplyswitching device while retaining the other of the displacement controldevice and the fluid-supply switching device.

Therefore, due to the elastic element, which requires no complicateddesign (such as to be required for the above link element forcorresponding to the link ratio difference) for corresponding to thedifference between the movable range of the displacement control deviceand the shiftable range of the fluid-supply switching device, thecushion mechanism can be simple and inexpensive.

These, further and other objects, features and advantages will appearmore frilly from the following description with reference toaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a four-wheel drive working vehicle (lawntractor) equipped with a main (rear) hydrostatic transaxle 3transmitting power to a sub (front) transaxle 55 through a mechanicaltransmission device including a propeller shaft 52 (and a mechanicaldrive-mode change clutch 29).

FIG. 2 is a sectional side view of main hydrostatic transaxle 3.

FIG. 3 is a cross sectional view taken along A-A line of FIG. 2.

FIG. 4 is a cross sectional view taken along B-B line of FIG. 2.

FIG. 5 is a cross sectional view taken along C-C line of FIG. 2.

FIG. 6 is a front vide of main hydrostatic transaxle 3.

FIG. 7 is a cross sectional view taken along D-D line of FIG. 4.

FIG. 8 is a cross sectional view taken along E-E line of FIG. 3.

FIG. 9 is a right side view of a front portion of main hydrostatictransaxle 3.

FIG. 10 is a fragmentary sectional side view of main hydrostatictransaxle 3, showing mechanical drive-mode change clutch 29 therein.

FIG. 11 is a hydraulic circuit diagram of the vehicle of FIG. 1 withmain hydrostatic transaxle 3.

FIG. 12 is a side view of a four-wheel drive working vehicle (lawntractor) equipped with a main (rear) hydrostatic transaxle 35 adapted totransmit power to a sub (front) transaxle 138 through a hydraulictransmission device including fluid pipes 136 and 137 (and a drive-modechange valve 135).

FIG. 13 is a sectional side view of main hydrostatic transaxle 35.

FIG. 14 is a fragmentary sectional side view of main hydrostatictransaxle 35, showing drive-mode change valve 135 therein.

FIG. 15 is a front view of main hydrostatic transaxle 35.

FIG. 16 is a cross sectional view taken along F-F line of FIG. 13.

FIG. 17 is a sectional rear view of a duct plate 154 of main hydrostatictransaxle 35.

FIG. 18 is a cross sectional view taken along G-G line of FIG. 13.

FIG. 19 is a right side view of a front portion of main hydrostatictransaxle 35, showing a linkage system 189 setting a drive-mode changeoperation arm 157 at a four-wheel drive mode position.

FIG. 20 is a right side view of the front portion of main hydrostatictransaxle 35, showing linkage system 189 setting drive-mode changeoperation arm 157 at a two-wheel drive mode position.

FIG. 21 is a perspective view of a linkage between a sub-speed controllever 174 and a sub-speed control arm 172.

FIG. 22 is a hydraulic circuit diagram of the vehicle of FIG. 12 withmain hydrostatic transaxle 35.

FIG. 23 is a sectional plan view of a front portion of main hydrostatictransaxle 35, showing drive-mode change valve 135 with an alternativefluid passage structure for supplying fluid to drive-mode change valve135.

FIG. 24 is a sectional plan view of a front portion of main hydrostatictransaxle 35, showing an alternative linkage system 212 interposedbetween sub-speed control arm 172 and drive-mode change operation arm157.

FIG. 25 is a right side view of a front portion of main hydrostatictransaxle 35, showing linkage system 212 setting drive-mode changeoperation arm 157 at the four-wheel drive mode position.

FIG. 26 is a right side view of a front portion of main hydrostatictransaxle 35, showing linkage system 212 setting drive-mode changeoperation arm 157 at the two-wheel drive mode position.

FIG. 27 is a hydraulic circuit diagram for supplying hydraulicallydriven devices with fluid from an auxiliary pump unit 213.

FIG. 28 is a sectional plan view of a charge pump 15 and auxiliary pumpunit 213.

FIG. 29 is a hydraulic circuit diagram for supplying hydraulicallydriven devices with fluid from an alterative double auxiliary pump unit236.

FIG. 30 is a sectional plan view of auxiliary pump unit 236.

FIG. 31 is a hydraulic circuit diagram of hydrostatic transaxle 3 forsupplying hydraulic driven devices with fluid from charge pump 15 and anauxiliary pump 401 in an alternative auxiliary pump unit 400.

FIG. 32 is a sectional plan view of a front portion of main hydrostatictransaxle 3, showing auxiliary pump unit 400 and the gear train forauxiliary pump unit 400 therein.

FIG. 33 is a fragmentary sectional side view of main hydrostatictransaxle 3 provided with alternative auxiliary pump unit 400, showingits portion incorporating charge pump 15.

FIG. 34 is a front view of a front unit 31 of main hydrostatic transaxle3, including auxiliary pump unit 400.

FIG. 35 is a front view partly in section of front unit 31, showing afluid passage structure and the gear train to auxiliary pump unit 400.

FIG. 36 is a plan view of front unit 31 including auxiliary pump unit400.

FIG. 37 is a rear view of auxiliary pump unit 400.

FIG. 38 is a sectional front view of auxiliary pump unit 400.

FIG. 39 is a sectional side view of auxiliary pump unit 400.

FIG. 40 is a sectional side view of main hydrostatic transaxle 3 or 35provided on its rear end with an alternative auxiliary pump unit 500.

FIG. 41 is a rear view of main hydrostatic transaxle 3 or 35 with rearauxiliary pump unit 500, including a sectional rear view of a rear PTOgear chamber 72 d.

FIG. 42 is a sectional rear view of main hydrostatic transaxle 3 or 35shown in FIGS. 40 and 41, showing a front PTO gear chamber 72 c.

FIG. 43 is a fragmentary sectional side view of transaxle 3 or 35showing an alternative structure for supporting a PTO clutch drive shaft505.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIGS. 1 and 12, each of two different working vehicles 1has the following common structure. Working vehicle 1 is provided at itsfront portion with an engine 14, and at its rear portion with a main(rear) hydrostatic transaxle 3 or 35 incorporating an HST 20 or 30.Transaxle 3 or 35 is provided with an input shaft 16, which projectsforward so as to receive power from engine 14 through a propeller shaft2 and universal joints, thereby driving HST 20 or 30 (see FIGS. 2 and13) for driving right and left rear drive wheels 4R and 4L disposed onright and left sides of transaxle 3 or 35.

A driver's seat 7 is disposed above transaxle 3 or 35, and a steeringwheel 8 is disposed in front of seat 7 so as to steer front wheels 5Rand 5L for turning of vehicle 1. A sub-speed control lever 174 isdisposed beside seat 7. A mid-mount mower 12 is disposed between frontwheels 5R and 5L and rear wheels 4R and 4L. Transaxle 3 or 35 isprovided at its lower portion with a mid PTO shaft 9, which projectsforward so as to be drivingly connected to a gearbox 12 a of mower 12through a propeller shaft 10. As drawn in dotted lines, main-speedcontrol pedal 305 is disposed at a fore-and-aft intermediate portion ofvehicle 1 and operatively connected to a movable swash plate 116 of ahydraulic pump 17 of HST 20 or 30 (see FIGS. 2 and 13) in transaxle 3 or35 so as to determine the traveling speed and direction of vehicle 1.

Vehicle 1 is provided with a rearward extended linkage (including rightand left lift arms 218 vertically rotatably mounted on the top oftransaxle 3 or 35 as shown in FIGS. 27 and 40 to 42) to be connected toa rear-mount working machine such as a rotary cultivator therebehind.Vehicle 1 is also provided with a hydraulic lift cylinder 11 betweentransaxle 3 or 35 and seat 7 so as to rotate lift arms 218 for raisingand lowering the rear-mount working machine. Transaxle 3 or 35 isprovided with a rear PTO shaft 13 projecting rearward so as to drive therear-mount working machine.

With respect to a different point between respective vehicles 1 of FIGS.1 and 12, vehicle 1 shown in FIG. 1 has a propeller shaft 52 withuniversal joints for transmitting power from rear (main) transaxle 3 toa front (sub) transaxle 55 for driving front wheels 5R and 5L. On thecontrary, vehicle 1 shown in FIG. 12 has hydraulic pressure fluid pipes136 and 137 for supplying fluid from rear (main) transaxle 35 to a front(sub) transaxle 138 for driving front wheels 5R and 5L.

Referring to FIGS. 2 to 11, hydrostatic transaxle 3 is configured so asto transmit power to front wheels 5R and 5L through a mechanicaltransmission device including propeller shaft 52 as shown in FIG. 1. Theconfiguration of hydrostatic transaxle 3 shown in FIGS. 2 to 11 and ahydraulic circuit system shown in FIG. 11 for vehicle 1 of FIG. 1 withtransaxle 3 will be described. Incidentally, FIGS. 41 and 42 arereferred to as they illustrate hydrostatic transaxle 3 on the assumptionthat a later-discussed auxiliary pump unit 500, a fluid passagestructure for auxiliary pump unit 500 and some different structures areignored.

As shown in FIG. 2 and others, a front casing part 96, a rear casingpart 97 and a rear cover 98 are joined to one another so as toconstitute a main casing of transaxle 3. The main casing of transaxle 3incorporates hydraulic pump 17 of HST 20, a differential unit 51differentially connecting right and left axles 4 aR and 4 aL to eachother, a deceleration gear train 50 interposed between an output shaft18 of HST 20 and differential unit 51, and a PTO gear train interposedbetween input shaft 16 and mid and rear PTO shafts 9 and 13.

As shown in FIG. 2 and others, a duct plate 48 is fixed onto a verticalfront surface of the main casing of transaxle 3, i.e., a vertical frontsurface of an upper portion of front casing part 96. A lower portion offront casing part 96 below duct plate 48 has a front wall 96 a (see FIG.8), from which mid PTO shaft 9 projects forward. A charge pump casing 76is fixed onto an upper portion of a vertical front surface of duct plate48 so as to incorporate a trochoidal charge pump 15, including an innerrotor 15 a fixed on input shaft 16 and an outer rotor 15 b surroundinginner rotor 15 a, as shown in FIGS. 2, 4 and 10. Input shaft 16 isinserted into the upper portion of front casing part 96 through chargepump casing 76, inner rotor 15 a of charge pump 15, and duct plate 48.Input shaft 16 projects forward from charge pump casing 76 so as to bedrivingly connected to engine 14 through propeller shaft 2 and theuniversal joints.

Referring to FIGS. 2, 4, 5, 7 and 11, to constitute HST 20 in transaxle3, duct plate 48 is formed with a vertical pump mounting surface 48 b onan upper portion of its vertical rear surface, as shown in FIG. 4, andhydraulic pump 17 is fitted onto pump mounting surface 48 b in frontcasing part 96 so as to be driven by input shaft 16. Also, duct plate 48is formed with a vertical motor mounting surface 48 c on a lower portionof its vertical front surface, as shown in FIG. 5, and a hydraulic motor19 with an output shaft 18 is fitted onto motor mounting surface 48 c ina motor casing 26 so as to be fluidly connected to hydraulic pump 17through main ducts 49 a and 49 b (a main passage 49 as a generic name)formed in duct plate 48.

To steplessly control the rotary speed and direction of output shaft 18,hydraulic pump 17 is provided with a movable pump swash plate 116, andhydraulic motor 19 is provided with a movable motor swash plate 117.Pump swash plate 116 is operatively connected to main-speed controlpedal 305 shown in FIG. 1, and motor swash plate 117 is operativelyconnected to sub-speed control lever 174 shown in FIG. 1.

As shown in FIGS. 2 and 11, a relief valve 40 is fitted downward intoduct plate 48 so as to regulate the pressure of fluid delivered fromcharge pump 15. As shown in FIG. 11, a resistance valve 41 is alsoconnected to the delivery passage from charge pump 15, so as to branchfluid from the delivery passage to a power steering control valve 67disposed on the outside of transaxle 3 through a fluid extraction port68 provided on the casing of transaxle 3 (in detail, on a front surfaceof charge pump casing 76 as shown in FIG. 6). Power steering controlvalve 67 is operatively connected to steering wheel 8 so as to controlfluid supply to a power steering cylinder 70 for steering front wheels5R and 5L. Power steering control valve 67 returns fluid drained frompower steering cylinder 70 to a fluid sump in a traveling gear chamber72 b through a fluid returning port 69 formed on the casing of transaxle3. As shown in FIG. 2, traveling gear chamber 72 b is formed in a frontlower portion of front casing part 96 so as to incorporate decelerationgear train 50 and differential unit 51. Alternatively, fluid returningport 69 is provided on charge pump casing 76, for instance, so as toreturn fluid into a pump chamber 72 a, similarly to that shown in FIG.35 illustrating later-discussed hydrostatic transaxle 3 (or 35) providedwith an alternative duct plate 348, an alternative charge pump casing276 and an auxiliary pump unit 400. Pump chamber 72 a is formed in anupper front portion of front casing part 96 above traveling gear chamber72 b so as to incorporate hydraulic pump 17.

As shown in FIG. 2, a reducing valve 42 is disposed in charge pumpcasing 76 so as to regulate pressure of fluid delivered from charge pump15. The fluid released from reducing valve 42 is supplied to a PTOswitching valve 39 of a later-discussed main PTO clutch 37. As shown inFIG. 7, a fore-and-aft duct 73 and a lateral duct 74 are bored in ductplate 48 between main ducts 49 a and 49 b. A pair of charge check valves43F and 43R are fitted into respective main ducts 49 a and 49 b so as tobe interposed between duct 74 and respective main ducts 49 a and 49 b.During circulation of fluid between hydraulic pump 17 and motor 19, oneof main ducts 49 a and 49 b is hydraulically depressed, and then,corresponding charge check valve 43F or 43R is opened to supply thepressure fluid regulated by reducing valve 42 into the depressed mainduct 49 a or 49 b.

Charge check valves 43F and 43R are provided with respective pushpins43Fa and 43Ra projecting outward from duct plate 48 so as to beconnected together to a bypass operation member 75 disposed on theoutside of (above) duct plate 48. To tow vehicle 1, a bypass operationdevice (not shown) is manipulated to push down pushpins 43Fa and 43Rathrough bypass operation member 75, so as to open both bypass valves 43Fand 43R, thereby draining fluid from main passage 49 and allowinghydraulic motor 19 to freely rotate following rotation of wheels 4R and4L.

As shown in FIGS. 7 and 11, charge check valve 43R is provided with abypassing orifice 44 so as to expand a neutral zone of hydraulic pump 17into its backward traveling range. As shown in FIGS. 2, 7, 10 and 11,additionally, a filter 46 and a check valve 45 are interposed betweenthe fluid sump of traveling gear chamber 72 b in front casing part 96(behind duct plate 48) and each of main ducts 49 a and 49 b. When engine14 is stationary and vehicle 1 is parked on a slope, fluid may leak outfrom the closed fluid circuit in duct plate 48 between hydraulic pump 17and motor 19. At this time, check valve (or valves) 45 is (are) openedto supply fluid from the fluid sump to the closed fluid circuit throughfilter (or filters) 46.

As shown in FIG. 3, 4, 7, 8 and 11, front casing part 96 has an openedright side wall 96 c, onto which a side cover 89 is fastened. As shownin FIG. 8, a filter mount portion 91 is formed on a right portion offront wall 96 a of front casing part 96, and a filter 90 is mounted ontofilter mount portion 91. Filter 90 has an inlet port (not shown) fluidlyconnected to the fluid sump in traveling gear chamber 72 b. Right sidewall 96 c and side cover 89 joined to each other are formed therebetweenwith respective fluid grooves 96 d and 89 a, which are joined to eachother so as to constitute a fluid duct 92, as shown in FIGS. 3 and 4.Filter 90 has an outlet port 90 a fluidly connected to a lower end offluid duct 92. As shown in FIG. 4, a fluid duct 96 e is extended forwardfrom an upper portion of fluid duct 92 (fluid groove 96 d) in frontcasing part 96, a suction port 76 a to charge pump 15 is formed incharge pump casing 76, and a connection duct 48 a is formed in ductplate 48 interposed between charge pump casing 76 and front casing part96, so that fluid duct 96 e is opened to suction port 76 a throughconnection duct 48 a.

As shown in FIGS. 4, 7, 9 and 11, a fluid extraction port 94 is fittedonto duct plate 48 and fluidly connected to connection duct 48 a, so asto extract fluid for a working machine. The casing of transaxle 3 (ductplate 48) is provided with a fluid returning port 95 for returning fluidto the fluid sump of traveling gear chamber 72 b in the casing oftransaxle 3 (i.e., front casing part 96).

The casing of transaxle 3 (i.e., front casing part 96) is formed thereinwith a pump chamber 72 a incorporating hydraulic pump 17. Whiletransaxle 3 is driven, the fluid temperature increased in traveling gearchamber 72 b is smaller than that in pump chamber 72 a. Due to the aboveconfiguration, charge pump 15 for supplying fluid to HST 20 sucks fluidfrom the fluid sump in traveling gear chamber 72 b through filter 90,fluid ducts 92 and others, so as to restrain the increased temperatureof fluid circulated in HST 20, thereby improving the durability of HST20. Further, filter 90 and its surrounding implements are concentratedon or in front casing part 96 without requiring an additional pipe. Dueto such a simple, compact and inexpensive duct structure, the fluid intraveling gear chamber 72 b is distributed between HST 20 and theexternal hydraulically driven implements.

As shown in FIGS. 2 and 3, output shaft 18 is extended rearward intotraveling gear chamber 72 b in front casing part 96 through duct plate48. A small bevel pinion 21 is fixed on a rear end of output shaft 18 infront casing part 96, and meshes with a large bevel gear 23 on a lateralcounter shaft 22 supported in front casing part 96. A gear 24 is formedon an outer peripheral surface of counter shaft 22 outward from gear 23.In this way, gears 21, 22 and 23 constitute deceleration gear train 50disposed in traveling gear chamber 72 b.

As shown in FIGS. 3, differential unit 51 is disposed in traveling gearchamber 72 b so as to differentially connect proximate ends of right andleft axles 4 aR and 4 aL to each other. As shown in FIGS. 3, 41 and 42,side cover 89 journals right axle 4 aR through a bearing, and frontcasing part 96 journals left axle 4 aL through a bearing. A pair ofright and left rear axle casings 6R and 6L are fixed onto side cover 89and the left side surface of front casing part 96, respectively, so asto support respective axles 4 aR and 4 aL. Distal ends of axles 4 aR and4 aL project outward from respective rear axle casings 6R and 6L so asto be formed into flanges 4 b onto which respective rear wheels 4R and4L are fixed.

As shown in FIG. 3, differential unit 51 includes a differential cage59, on which a bull gear 25 serving as an input gear of differentialunit 51 is fixed so as to mesh with gear 24 formed on counter shaft 22.The proximate ends of axles 4 aR and 4 aL are inserted into differentialcage 59 so as to be fixedly provided thereon with respectivedifferential side gears 60R and 60L. A differential pinion shaft 61 issupported in differential cage 59 in perpendicular to axles 4 aR and 4aL, and opposite differential pinions 62 are pivoted on differentialpinion shaft 61. Each differential pinion 62 meshes with bothdifferential side gears 60R and 60L. In this way, differential unit 51is configured so as to receive power from output shaft 18 throughdeceleration gear train 50, and to distribute the power between rightand left rear wheels 4R and 4L.

As shown in FIG. 3, differential unit 51 is provided with a differentiallock mechanism 63. In this regard, differential cage 59 is formed with aboss 59 a axially extended on one (left) axle 4 aL. A differential lockslider 65 with an annular groove 65 a is axially slidably fitted on boss59 a. A fork 66 is fitted into groove 65 a of differential lock slider65, and is operatively connected to a differential locking manipulator(not shown). A plurality of lock pins 64 a are axially extended from aproximal side surface of differential lock slider 62, and slidablypenetrate differential cage 59, so that lock pins 64 a can be insertedinto respective recesses 60 a formed on one (left) differential sidegear 60L.

Differential lock slider 65 is normally disposed at a differentialposition so as to remove lock pins 64 a from recesses 60 a, therebyallowing axles 4 aR and 4 aL to differentially rotate. When thedifferential lock operation device is operated for differential locking,differential lock slider 65 is slid to a differential lock position soas to engage lock pins 64 a into recesses 60 a, thereby differentiallyunrotatably locking axles 4 aR and 4 aL to each other.

As shown in FIGS. 1, 2 and 10, motor casing 26 is fixed to the lowerfront surface of duct plate 48 and extended forward so as to incorporatehydraulic motor 19. A drive-mode change clutch casing 27 is fixed onto afront surface of motor casing 26. A front end of output shaft 18 isinserted into drive-mode change clutch casing 27, and fitted into a rearend portion of a coaxial front-wheel driving output shaft 28.Front-wheel driving output shaft 28 is exposed at its front end so as tobe drivingly connected to a differential unit 53 in front transaxle 55through propeller shaft 52 and the universal joints.

As shown in FIG. 11, in front transaxle 55, right and left differentialoutput shafts 5 aR and 5 aL are differentially connected at theirproximal ends to each other through differential unit 53. Right and leftsteerable transmission units 54, supporting respective axles 5 bR and 5aL, are steerably fitted onto right and left ends of front transaxle 55,so as to be drivingly and steerably connected to respective differentialoutput shafts 5 aR and 5 aL. Front wheels 5R and 5L are fixed on distalends of respective axles 5 bR and 5 aL, so as to serve as steerabledrive wheels.

A mechanical drive-mode change clutch 29 is interposed between outputshaft 18 and front-wheel driving output shaft 28 in drive-mode changeclutch casing 27. In this regard, a spline hub 29 a is axially andperipherally immovably spline-fitted on the outer peripheral surface ofoutput shaft 18 just behind front-wheel driving output shaft 28. Acylindrical clutch slider 56 is axially slidably spline-fitted on anouter peripheral surface of front-wheel driving output shaft 28, so thatit can be spline-fitted onto an outer peripheral spline of output shaft18. Further, clutch slider 56 is formed on its inner peripheral surfacewith a pair of front and rear grooves 56 a, which are juxtaposed in theaxial direction for defining a two-wheel drive mode position (clutch-offposition) and a four-wheel drive mode position (clutch-on position),respectively. Clutch slider 56 is operatively connected through a forkor the like to a drive-mode change manipulator (not shown). Front-wheeldriving output shaft 28 is penetrated by a diametric hole 28 a, intowhich a compressed spring 58 and a pair of detent balls 57 disposed onopposite ends of spring 58 are fitted.

By rearward sliding clutch slider 56, detent balls 57 are fitted intorear groove 56 a of clutch slider 56 defining the four-wheel drive modeposition, and clutch slider 56 fitted on front-wheel driving outputshaft 28 is also spline-fitted on spline hub 29 a so as to rotatablyintegrally engage front-wheel driving output shaft 28 to output shaft18, thereby transmitting the rotary force of output shaft 18 of HST 20to front wheels 5L and 5R. By forward sliding clutch slider 56, detentballs 57 are fitted into front groove 56 a of clutch slider 56 definingthe two-wheel drive mode position, and clutch slider 56 is separatedfrom spline hub 29 a and fitted on only front-wheel driving output shaft28, so as to isolate front-wheel driving output shaft 28 from the rotaryforce of output shaft 18, thereby preventing the output force of HST 20from being transmitted to front wheels 5L and 5R.

As shown in FIG. 2, a vertical partition wall 96 b is formed in an upperportion of front casing part 96 so as to define a rear end of pumpchamber 72 a, and a vertical partition wall 96 h is formed in a lowerportion of front casing part 96 under partition wall 96 b so as todefine a rear end of traveling gear chamber 72 b. Rear casing part 97 isfastened to a rear end surface of front casing part 96 so as to cover arear end opening of front casing part 96. A front PTO gear chamber 72 cis formed between front and rear casing parts 96 and 97 behind partitionwalls 96 b and 96 h, i.e., behind chambers 72 a and 72 b.

As shown in FIGS. 2, 4, 8 and 11, input shaft 16 is extended rearwardfrom hydraulic pump 17 and journalled by partition wall 96 b through abearing. In front PTO gear chamber 72 c, a PTO clutch shaft 32 isdisposed coaxially to input shaft 16 and journalled by rear casing part97 through a bearing. The rear end of input shaft 16 is relativelyrotatably fitted into a front end portion of PTO clutch shaft 32. A mainPTO clutch 37 is disposed in an upper portion of front PTO gear chamber72 c just behind partition wall 96 b so as to be interposed betweeninput shaft 16 and PTO clutch shaft 32.

In front PTO gear chamber 72 c, a rotary member 33 is fixed on inputshaft 16 in front of PTO clutch shaft 32, and a rotary drum 36 is fixedon PTO clutch shaft 32 and extended forward around rotary member 33.Friction disks, axially slidably fitted onto an outer peripheral surfaceof rotary member 33, and friction disks, axially slidably fitted onto aninner peripheral surface of the forward extended portion of rotary drum36, are alternately aligned. A piston 37 b is disposed between therearmost friction disk and a rear boss portion of rotary drum 36 fixedon PTO clutch shaft 32, so that it can be pushed forward by hydraulicpressure to press the friction disks against one another. A spring 37 ais wound around a center boss of piston 37 b on PTO clutch shaft 32 soas to bias piston 37 b rearward against the hydraulic pressure forforward moving piston 37 b. In this way, rotary member 33, rotary drum36, the friction disks between rotary member 33 and rotary drum 36,spring 37 a and piston 37 b constitute main PTO clutch 37 interposedbetween input shaft 16 and PTO clutch shaft 32.

A fluid duct 77 is formed in PTO clutch shaft 32. Fluid duct 77 isopened at one (front) end thereof to a clutch pressure fluid chamber 81(see FIG. 4) behind piston 37 b. Rear casing part 97 is formed with afluid chamber 38 behind the rear end of PTO clutch shaft 32. Fluid duct77 is opened at the other (rear) end thereof to fluid chamber 38.

As shown in FIG. 4, a brake 79 is disposed sidewise from main PTO clutch37 so as to prevent disengaged main PTO clutch 37 from inertiallyrotating. A laterally penetrating hole 89 b in side cover 89 is joinedto a recess 96 g formed on an outer surface of right side wall 96 c offront casing part 96, and a brake accumulator cover 99 is fastened toside cover 89 by bolts 100 so as to cover the opening of hole 89 b,thereby constituting a brake accumulator chamber 83 serving as anaccumulator for brake 79.

A connection hole is formed in side wall 96 c so as to connect front PTOgear chamber 72 c around main PTO clutch 37 to recess 96 g of brakeaccumulator chamber 83. A sleeve 88 is fitted in this connection hole. Apiston 85 is slidably fitted in recess 96 g. A center axial shaft 84 isextended from piston 85 in opposite directions, i.e., inward and outwardin the lateral direction of transaxle 3, so as to be axially slidableintegrally with piston 85. The inward extended portion of shaft 84 isaxially slidably fitted through sleeve 88, and extended into front PTOgear chamber 72 c so as to be fixedly provided on its proximal end witha friction member 86 facing the outer peripheral surface of rotary drum36. Springs 87 having different spring forces are concentrically woundedaround the outward extended portion of shaft 84 in a space 83 b of brakeaccumulator chamber 83 outward from piston 85 so as to bias piston 85and shaft 84 toward main PTO clutch 37.

Brake accumulator chamber 83 has a space 83 a between piston 85 andright side wall 96 c of front casing part 96 in recess 96 g. A fluidduct 96 f is formed in right side wall 96 c and opened at its front endto space 83 a. Fluid duct 96 f is extended rearward so as to beconnected to fluid chamber 38 through a fluid duct 97 a formed in rearcasing part 97. Mutually joined fluid ducts 96 f and 97 a constitute afluid duct 78.

As shown in FIG. 2, fluid chamber 38 is fluidly connected to PTOswitching valve 39 for controlling main PTO clutch 37. PTO switchingvalve 39 is a three-port and two-position electromagnetic valve fittedon an external surface of rear casing part 97. Referring to FIG. 11, apump port of PTO switching valve 39 is connected to a drain port ofreducing valve 42 in charge pump casing 76, as mentioned above, so as toreceive fluid drained from reducing valve 42. A relief valve 80 isfitted into rear casing part 97 so as to regulate the pressure of fluidfrom reducing valve 42 to PTO switching valve 39.

In vehicle 1, a switch for switching main PTO clutch 37 is disposedadjacent to driver's seat 7, and is operatively connected to PTOswitching valve 39 for selecting either engagement or disengagement ofmain PTO clutch 37. To disengage main PTO clutch 37, PTO switching valve39 is set at a position as shown in FIG. 11, so as to drain fluid to afluid sump 101 (any fluid sump in transaxle 3, for instance) from thedrain port of reducing valve 42, and from fluid chamber 38. The fluiddrained from fluid chamber 38 means the fluid drained from clutchpressure fluid chamber 81 through fluid duct 77 and from space 83 a ofbrake accumulator chamber 83 through fluid duct 78. In main PTO clutch37, due to the draining of fluid from clutch pressure fluid chamber 81,piston 37 b is pushed away from the friction disks by the force ofspring 37 a, so as to isolate PTO clutch shaft 32 from the rotary forceof input shaft 16, i.e., disengage main PTO clutch 37. Simultaneously,in brake 79, due to the draining of fluid from space 83 a of brakeaccumulator chamber 83, piston 85 is pushed toward main PTO clutch 37 bythe force of springs 87, so as to press friction member 86 againstrotary drum 36, thereby braking PTO clutch shaft 32 with rotary drum 36.Accordingly, mid PTO shaft 9 and rear PTO shaft 13 to be driven by PTOclutch shaft 32 are quickly stopped and prevented from inertiallyrotating.

To engage main PTO clutch 37, PTO switching valve 39 is set at the otherposition shown in FIG. 11, so as to supply fluid from the drain port ofreducing valve 42 to fluid chamber 38, thereby supplying the fluid toclutch pressure fluid chamber 81 through fluid duct 77, and to space 83a of brake accumulator chamber 83 through fluid duct 78. In main PTOclutch 37, due to the supply of fluid to clutch pressure fluid chamber81, piston 37 b is pushed toward the friction disks against the force ofspring 37 a and press the friction disks against one another, so as totransmit the rotary force of input shaft 16 to PTO clutch shaft 32,i.e., to engage main PTO clutch 37. Simultaneously, in brake 79, due tothe supply of fluid to space 83 a of brake accumulator chamber 83,piston 85 is pushed away from main PTO clutch 37 against the force ofsprings 87, so as to separate friction member 86 from rotary drum 36,thereby releasing PTO clutch shaft 32 from the braking force of brake79.

As shown in FIGS. 2 and 42, in front PTO gear chamber 72 c, a countershaft 102 is disposed horizontally under main PTO clutch 37, and isjournalled at front and rear portions thereof by partition wall 96 h andrear casing part 97 through respective bearings. An idle gear 13 isfixed on counter shaft 102 and meshes with a gear 34 formed on rotarydrum 36 of main PTO clutch 37. Mid PTO shaft 9 is journalled bypartition wall 96 h, and extended rearward from partition wall 96 h. Asleeve 110 is spline-fitted on an outer peripheral surface of therearward extended portion of mid PTO shaft 9. A gear 104 is relativelyrotatably fitted on sleeve 110 through a bearing, and meshes with idlegear 103.

Gear 104 serves as an input gear of a later-discussed sub PTO clutch112.

As shown in FIG. 2, a rear PTO casing 105 is fixed onto rear casing part97 so as to project rearward from rear casing part 97. Alternatively,referring to FIGS. 40 and 41, a rearward projecting portion 97 e isintegrally formed on rear casing part 97 so as to serve as rear PTOcasing 105. Rear cover 98 is fixed to a rear end surface of rear PTOcasing 105 so as to cover a rear end opening of rear PTO casing 105, sothat a rear PTO gear chamber 72 d for incorporating a rear PTOdeceleration gear train 106 is formed in rear PTO casing 105 betweenrear casing part 97 and rear cover 98 behind front PTO gear chamber 72c.

Rear PTO shaft 13 is disposed above mid PTO shaft 9, journalled at frontand rear portions thereof by rear PTO casing 105 and rear cover 98through respective bearings, and extended rearward from rear cover 98.Rear PTO deceleration gear train 106 is interposed betweenlater-discussed sub PTO clutch 112 and rear PTO shaft 13. As best shownin FIGS. 40 and 41, rear PTO deceleration gear train 106 includes a gear13 a, a double gear 107 and a gear 109. Gear 13 a is fixed on rear PTOshaft 13 in rear PTO casing 105. Gear 109 is spline-fitted on a supportshaft 108. Support shaft 108 is coaxially extended rearward from mid PTOshaft 9, and is journalled by rear cover 98 through bearings. Doublegear 107 is provided on a counter shaft 107 c supported in rear PTO gearchamber 72 d between rear casing part 97 and rear cover 98. Double gear107 includes a pair of rotatably integral large and small gears 107 aand 107 b. Large gear 107 a meshes with gear 109, and small gear mesheswith gear 13 a.

Gear 109 has a center boss portion, which is extended forward toward midPTO shaft 9 and has a spline-toothed front end 109 a. Sleeve 110 and acenter boss portion of gear 104 are extended rearward toward supportshaft 108, so that sleeve 110 has a spline-toothed rear end 110 a closeto spline-toothed front end 109 a of gear 109, and gear 104 has aspline-toothed rear end 104 a just in front of spline-toothed rear end10 a, i.e., opposite to spline-toothed front end 109 a with respect tospline-toothed rear end 110 a. A cylindrical clutch slider 111 isaxially slidably spline-fitted on spline-toothed rear end 110 a ofsleeve 110. On the inner peripheral surface of clutch slider 111, aforemost spline-tooted portion 111 a, a rearward spline-toothed portion111 b and a rearmost spline-toothed portion 111 c are formed, andforemost spline-toothed portion 111 a is spaced from rearwardspline-toothed portion 111 b. A shifter fork 113 is engaged onto clutchslider 111. In this way, gears 104 and 109, sleeve 110, clutch slider111 and shifter fork 113 constitute sub PTO clutch 112.

By optionally operating shifter fork 113, clutch slider 111 is slidablyshifted among three positions, i.e., front, middle and rear positions.Foremost spline-toothed portion 111 a constantly meshes withspline-toothed rear end 104 a of gear 104 regardless of slide of clutchslider 111. When clutch slider 111 is disposed at the front position,rearward spline-toothed portion 111 b meshes with spline-toothed rearend 104 a, and rearmost spline-toothed portion 111 c meshes withspline-toothed rear end 110 a, so as to drivingly engage sleeve 110 togear 104 and to drivingly disengage gear 109 from gear 104, therebydriving only mid PTO shaft 9. When clutch slider 111 is disposed at themiddle position, rearward spline-toothed portion 111 b meshes withspline-toothed rear end 10 a, and rearmost spline-toothed portion 111 cmeshes with spline-toothed rear end 109 a, so as to drivingly engageboth sleeve 110 and gear 109 to gear 104, thereby driving both mid PTOshaft 9 and rear PTO shaft 13. When clutch slider 111 is disposed at therear position, rearward spline-toothed portion 111 b meshes withspline-toothed rear end 109 a, and rearmost spline-toothed portion 111 cis separated rearward from spline-toothed rear end 109 a, so as todrivingly engage gear 109 to gear 104 and to drivingly disengage sleeve110 from gear 104, thereby driving only rear PTO shaft 13.

HST 20 will be detailed. As shown in FIGS. 3 and 4, in pump chamber 72 aformed in front casing part 96, hydraulic pump 17 includes: a valveplate 298 fixed on pump mounting surface 48 b of duct plate 48; acylinder block 114 slidably rotatably fitted on valve plate 298; andpistons 115 reciprocally fitted into cylinder block 114 throughrespective springs. Cylinder block 114 is relatively unrotatably engagedonto input shaft 16 disposed on its rotary axis. Pistons 115 abut attheir heads against a thrust bearing 116 a of movable pump swash plate116 through which input shaft 16 is freely rotatably extended rearward.

Pump swash plate 116 has a pair of lateral opposite trunnion shafts 116b. Left trunnion shaft 116 b is rotatably supported by a left side wallof front casing part 96, and right trunnion shaft 116 b is rotatablysupported by side cover 89. Right trunnion shaft 116 b is extendedoutward from side cover 89 so as to be fixedly provided on its distalend with a main-speed control arm 121. Main-speed control arm 121 isoperatively connected to main-speed control pedal 305 through a linkmember such as a connection rod. A support pin 89 c projects outwardfrom the outer side surface of side cover 89. Main-speed control arm 121is extended downward from trunnion shaft 116 b, and a shock absorber 112is interposed between a lower end of main-speed control arm 121 andsupport pin 89 c, so as to moderate the neutral returning of pump swashplate 116 when main-speed control pedal 305 having been depressed isreleased.

A neutral returning spring 118 is wound around right trunnion shaft 116b in pump chamber 72 a. Both end portions of spring 118 are twisted tocross each other, and are extended in one direction. A movable pin 119is fixed on a side surface of pump swash plate 116, and a fixedeccentric pin 120 is extended from an inner surface of side cover 89, sothat pins 119 and 120 are pinched between the both end portions ofspring 118 when pump swash plate 116 is disposed at the neutralposition. As pump swash plate 116 is tilted from the neutral position,movable pin 119 pushes one end portion of spring 118 away from the otherend portion retained by fixed eccentric pin 120 so as to cause theneutral returning force of spring 118 for automatically returning pumpswash plate 116 to the neutral position when pump swash plate 116 isreleased from an operation force. Eccentric pin 120 can be loosened fromside cover 89 and rotated to adjust its position defining the neutralposition of pump swash plate 116 relative to the neutral position ofmain-speed control pedal 305.

As shown in FIGS. 5, 6 and 9, in motor casing 26, hydraulic motor 19includes: a valve plate 299 fixed on motor mounting surface 48 c of ductplate 48; a cylinder block 123 slidably rotatably fitted on valve plate299; and pistons 124 reciprocally fitted into cylinder block 123 throughrespective springs. Cylinder block 123 is relatively unrotatably engagedonto output shaft 18 disposed on its rotary axis. Pistons 124 abut attheir heads against a thrust bearing 300 of movable motor swash plate117 through which output shaft 18 is freely rotatably extended forward.

A side cover 126 is fixed onto a right side surface of motor casing 26so as to cover the right opening of motor casing 26. A lateralhorizontal control shaft 301 is rotatably supported by side cover 126. Acontrol arm 301 a is formed on an inner end of control shaft 301 inmotor casing 26, and connected to cradle-type motor swash plate 117through a connection block 125. An L-shaped sub-speed control arm 127,including a forward extended restriction portion 127 a and an upwardextended operation portion 127 b, is fixed on a distal end of controlshaft 301 projecting outward from side cover 126.

A U-shaped restriction wall 126 a (when viewed in side) is formed onside cover 126 so as to have an upper wall portion 126 a 1 and a lowerwall portion 126 a 2. Restriction portion 127 a of sub-speed control arm127 is inserted into a spaced surrounded by U-shaped restriction wall126 a between upper and lower walls 126 a 1 and 126 a 2. Operationportion 127 b of sub-speed control arm 127 is operatively connected tosub-speed control lever 174 through a later-discussed connection rod173, so as to be rotatable between a low-speed position 129 and ahigh-speed position 130 according to rotation of sub-speed control lever174. More specifically, when restriction portion 127 a abuts againstupper wall portion 126 a 1 of restriction wall 126, operation portion127 b is disposed at low-speed position 129 for setting motor swashplate 117 at a position for determining a large displacement ofhydraulic motor 19. When restriction portion 127 a abuts against lowerwall portion 126 a 2 of restriction wall 126, operation portion 127 b isdisposed at high-speed position 130 for setting motor swash plate 117 ata position for determining a small displacement of hydraulic motor 19.The linkage structure between sub-speed control lever 174 and sub-speedcontrol arm 127 will be detailed in later description of transaxle 35referring to FIG. 21.

A hole 127 c is bored in restriction portion 127 a of sub-speed controlarm 127, and a tapped hole 126 b is formed in side cover 126 so as tocorrespond to hole 127 c. A bolt 153 is screwed into tapped hole 126 bthrough hole 127 c so as to fix sub-speed control arm 127 before vehicle1 having been completely assembled is shipped.

Referring to FIGS. 13 to 22, main (rear) hydrostatic transaxle 35 isconfigured so as to transmit power to sub (front) transaxle 138 fordriving front wheels 5R and 5L through a hydraulic transmission deviceincluding pipes 136 and 137 as shown in FIG. 12. The configuration ofhydrostatic transaxle 35 shown in FIGS. 13 to 22 and a hydraulic circuitsystem shown in FIG. 22 for vehicle 1 of FIG. 12 will be described.However, description of components and parts, which are equivalent tothose designated by the same reference numerals in FIGS. 1 to 11, willbe omitted. Further, FIGS. 13 to 21 illustrates neither a main casing oftransaxle 35, including front casing part 96, rear casing part 97 andrear cover 98 joined to one another, nor the interior structure of themain casing of transaxle 35, on the assumption that the main casing oftransaxle 35 is configured similar to the main casing of transaxle 3 soas to incorporate hydraulic pump 17 of an HST 30, differential unit 51,deceleration gear train 50 between an output shaft 155 of HST 30 anddifferential unit 51, and the drive train between input shaft 16 and midand rear PTO shafts 9 and 13.

Incidentally, with respect to later-discussed alternative main (rear)hydrostatic transaxles shown in FIGS. 23 to 42, description orillustration of components and parts, which are equivalent to thosedesignated by the same reference numerals in FIGS. 1 to 22, will also beomitted.

A duct plate 154, as shown in FIGS. 13, 15, 17 to 19, is fixed onto thefront end of front casing part 96 (not shown). In front casing part 96,hydraulic pump 17 is fitted on a vertical upper rear pump mountingsurface 154 b of duct plate 154, and hydraulic motor 19 is fitted on avertical lower front motor mounting surface 154 c of duct plate 154.Duct plate 154 is formed therein with a part of a closed fluid circuit130 through which hydraulic motor 19 is fluidly connected to hydraulicpump 17, thereby constituting HST 30 in transaxle 35. Hydraulic pump 17disposed in the main casing of transaxle 35 requires no additionalexclusive casing. Alternatively, hydraulic pump 17 may be fitted on thefront surface of duct plate 154 so as to be disposed in a pump casingextended forward from duct plate 154, and the pump casing may be formedintegrally with motor casing 26 incorporating hydraulic motor 19.

Closed fluid circuit 130 includes a pair of fluid passages: one to behigher-pressurized for forward traveling; and the other to behigher-pressurized for backward traveling. A fluid duct 140 is bored induct plate 154 and interposed between hydraulic pump 17 and motor 19fitted on duct plate 154, so as to solely serve as the fluid passage tobe higher-pressurized for forward traveling. The fluid passage to behigher-pressurized for backward traveling includes a drive-mode changevalve 135 disposed in rear transaxle 35. Hydraulic pressure fluid pipes136 and 137 are extended from drive-mode change valve 135 to fronttransaxle casing 138 so as to supply fluid to a pair of left and righthydraulic motors 133 and 134 disposed in front transaxle 138 for drivingrespective front wheels 5L and 5R, as shown in FIG. 22.

In front transaxle 138, a fluid passage 139, on which hydraulic motors133 and 134 are provided in parallel, is interposed between pipes 136and 137. A fluid passage 139 includes a bifurcated passage 139 a, whichis extended from pipe 136 and bifurcated to hydraulic motors 133 and134, and a bifurcated passage 139 b, which is extended from pipe 137 andbifurcated to hydraulic motors 133 and 134.

Drive-mode change valve 135 is shiftable between a two-wheel drive modeposition and a four-wheel drive mode position. When drive-mode changevalve 135 is disposed at the two-wheel drive mode position, the fluidpassage to be higher-pressurized for backward traveling fluidly connectshydraulic motor 19 to hydraulic pump 17 without hydraulic motors 133 and134, thereby completing close fluid circuit 130 within only rearhydrostatic transaxle 35. When drive-mode change valve 135 is disposedat the four-wheel drive mode position, the fluid passage to behigher-pressurized for backward traveling is extended to the pair ofparallel hydraulic motors 133 and 134 between hydraulic motor 19 andhydraulic pump 17, whereby closed fluid circuit 130 is configured sothat hydraulic motor 19 and the pair of hydraulic motors 133 and 134 arefluidly connected in series to hydraulic pump 17, and hydraulic pump 19distributes fluid between parallel hydraulic motors 133 and 134 in fronttransaxle 138.

Alternatively, in closed fluid circuit 130, it is not limited which ofthe pair of passages extended from hydraulic pump 17 ishigher-pressurized for forward traveling. In this regard, the above andlater mentioned relation between the passages extended from hydraulicpump 17 may be reversed.

A configuration for supplying fluid from hydraulic pump 17 to hydraulicmotor 19 and to the pair of hydraulic motors 133 and 134 will bedescribed with reference to FIGS. 13 to 18 and 22. Duct plate 154 isbored with a pair of kidney ports 154 b 1 and 154 b 2 opened at pumpmounting surface 154 b. Duct plate 154 is also bored with a pair ofkidney ports 154 c 1 and 154 c 2 opened at motor mounting surface 154 c.Fluid duct 140 (serving as the fluid passage to be higher-pressurizedfor forward traveling) bored in duct plate 154 is interposed betweenkidney ports 154 b 1 and 154 c 1.

Outwardly opened ports 149 and 147 are fitted onto duct plate 154. Afluid duct 144 is bored in duct plate 154, and interposed between kidneyport 154 b 2 and port 149. A fluid duct 141 is bored in duct plate 154,and interposed between kidney port 154 c 2 and port 147.

Instead of drive-mode change clutch casing 27 incorporating drive-modechange clutch 29, drive-mode change valve 135 is provided onto the frontsurface of motor casing 26 incorporating hydraulic motor 19. In thisregard, a valve casing 135 a is fixed onto the front surface of motorcasing 26 by bolts 164, and a rotary valve shaft 158 is rotatably fittedin a laterally extended valve chamber 135 b bored in valve casing 135 a.Rotary valve shaft 158 projects rightwardly outward from valve casing135 a so as to be fixedly provided thereon with a drive-mode changeoperation arm 157. Outwardly opened ports 150 and 148 are fitted ontovalve casing 135 a, and fluidly connected to valve chamber 135 b invalve casing 135 a. A fluid pipe 145 is interposed between port 149 onduct plate 154 and port 150 on valve casing 135 a. A fluid pipe 142 isinterposed between port 147 on duct plate 154 and port 148 on valvecasing 135 a. Further, outwardly opened ports 151 and 152 are fittedonto valve casing 135 a so as to be connected to respective fluid pipes136 and 137 extended to front transaxle 138.

In this way, to constitute the fluid passage to be higher-pressurizedfor backward traveling, kidney port 154 b 2, fluid duct 144, port 149,fluid pipe 145 and port 150 are interposed between hydraulic pump 17 anddrive-mode change valve 135, and on the other hand, kidney port 154 c 2,fluid duct 141, port 147, fluid pipe 142 and port 148 are interposedbetween hydraulic motor 19 and drive-mode change valve 135.

A diametrically larger body of rotary valve shaft 158 slidably rotatablyfitted in valve chamber 135 b serves as a rotary valve main body 158 d.A lateral middle portion of rotary valve main body 158 d is notched soas to serve as a valve port portion 158 a having a pair of parallel flatsurfaces 158 c disposed symmetrically with respect to a center axis 162of rotary valve shaft 158. Spaces enclosed by respective flat surfaces158 c and the inner peripheral surface of valve chamber 135 b serve as apair of opposite valve ports 135 d. A pair of left and right annulargrooves 158 e are formed on rotary valve main body 158 d symmetricallywith respect to valve port portion 158 a. An axial drain duct 158 f isbored in rotary valve main body 158 d on center axis 162, and radialholes are extended from drain duct 158 f to respective annular grooves158 e. A drain port 135 c is bored in valve casing 135 a, opened todrain duct 158 f in valve chamber 135 b, and opened to a fluid sump 165in valve casing 135 a.

In valve casing 135 a, from the portion of valve chamber 135 bcorresponding to valve port portion 158 a, a fluid duct 135 e isextended rearward to port 150, a fluid duct 135 f is extended upward toport 148, a fluid duct 135 g is extended downward to port 151, and afluid duct 135 h is extended forward to port 152.

Due to such a configuration of rotary drive-mode change valve 135, whendrive-mode change operation arm 157 and rotary valve shaft 158 arerotated so as to locate valve port portion 158 a at a position 160 shownin FIG. 14, one valve port 135 d is opened to fluid ducts 135 f and 135e, so as to fluidly connect port 148 to port 150 through fluid duct 135f, valve port 135 d and fluid duct 135 e. Simultaneously, the othervalve port 135 d is opened to fluid ducts 135 g and 135 h, so as tofluidly connect port 151 to port 152 through fluid duct 135 g, valveport 135 d and fluid duct 135 h. That is, drive-mode change valve 135 isdisposed at the two-wheel drive mode position so as to fluidly connectfluid duct 144 to fluid duct 141 in duct plate 154 through drive-modechange valve 135 without supplying fluid to hydraulic motors 133 and 134in front transaxle 138. In other words, kidney port 154 b 2, fluid duct144, port 149, fluid pipe 145, port 150, fluid duct 135 e, valve port135 d, fluid duct 135 f, port 148, fluid pipe 142, port 147, fluid duct141 and kidney port 154 c 2 are fluidly connected in series to oneanother within only rear transaxle 35, so as to constitute the fluidpassage to be higher-pressurized for backward traveling in closed fluidcircuit 130 between hydraulic pump 17 and motor 19. Simultaneously, dueto the connection of fluid ducts 135 g and 135 h through the other valveport 135 d, a close circuit including the pair of hydraulic motors 133and 134 is made so as to be isolated from closed circuit 130 of HST 30,and to allow free rotation of hydraulic motors 133 and 134 followingrotation of front wheels 5L and 5R.

On the other hand, when drive-mode change operation arm 157 and rotaryvalve shaft 158 are rotated so as to locate valve port portion 158 a ata position 161 shown in FIGS. 13 and 22, one valve port 135 d is openedto fluid ducts 135 f and 135 h, so as to fluidly connect port 148 toport 152 through fluid duct 135 f, valve port 135 d and fluid duct 135h. Simultaneously, the other valve port 135 d is opened to fluid ducts135 e and 135 g, so as to fluidly connect port 150 to port 151 throughfluid duct 135 e, valve port 135 d and fluid duct 135 g. That is,drive-mode change valve 135 is disposed at the four-wheel drive modeposition so as to fluidly connect fluid duct 144 in duct plate 154 tofluid pipe 136 through drive-mode change valve 135 and to fluidlyconnect fluid duct 141 in duct plate 154 to fluid pipe 137 throughdrive-mode change valve 135, thereby supplying fluid to hydraulic motors133 and 134 in front transaxle 138. In other words, kidney port 154 b 2,fluid duct 144, port 149, fluid pipe 145, port 150, fluid duct 135 e,valve port 135 d, fluid duct 135 g, port 151, fluid pipe 136 andbifurcated passage 139 a are sequentially connected to one another so asto constitute the fluid passage to be higher-pressurized for backwardtraveling, extended from hydraulic pump 17 in rear transaxle 35 to thepair of hydraulic pumps 133 and 134 in front transaxle 138.Simultaneously, bifurcated passage 139 b, fluid pipe 137, port 152,fluid duct 135 h, valve port 135 d, fluid duct 135 f, port 148, fluidpipe 142, port 147, fluid duct 141 and kidney port 154 c 2 aresequentially connected to one another so as to constitute the fluidpassage from the pair of hydraulic motors 133 and 134 in front transaxle138 to hydraulic motor 19 in rear transaxle 35.

In transaxle 35, hydraulic motor 19 is disposed in motor casing 26,sub-speed control arm 127 is supported onto side cover 126 attached tomotor casing 26 through control shaft 301, sub-speed control arm 127 isoperatively connected to sub-speed control lever 174 through connectionrod 173, and control shaft 301 is connected to motor swash plate 117,similar to those in transaxle 3.

A linkage system 189 for associating the drive-mode change operationwith the sub-speed control operation will be described with reference toFIGS. 13, 14, 18 to 20 and 22. A link arm 177 is fixed at its upperportion onto operation portion 127 b of sub-speed control arm 127, andis extended downward so as to be pivotally connected at its bottomportion to a tip of drive-mode change operation arm 157 through a linkrod 178, a link arm 179 and a link rod 180. In this way, linkage system189, including link arm 177, link rod 178, link arm 179 and link rod180, is interposed between sub-speed control arm 127 and drive-modechange operation arm 157.

A support plate 182 is fixed on side cover 126, and a pivot shaft 181projects laterally horizontally from support plate 182. Link arm 179 ispivoted on pivot shaft 181, so that link arm 179 has a short linkportion 179 a extended downward from pivot shaft 181 to be pivoted atits bottom end to link rod 180, and has a long link portion 179 bextended upward from pivot shaft 181 just opposite to short link portion179 a to be pivoted at its top end to link rod 178.

Referring to FIG. 19, linkage system 189 is configured so thatdrive-mode change operation arm 157 is disposed at a four-wheel drivemode position 184 for setting drive-mode change valve 135 (valve portportion 158 a) at four-wheel drive mode position 161 as shown in FIG. 13when sub-speed control arm 127 is disposed at low-speed position 129.Therefore, during low-speed traveling, vehicle 1 is automatically drivenby four wheels advantageously for traction or traveling on a rough road.

Referring to FIG. 20, when sub-speed control lever 174 is operated forhigh-speed traveling, operation portion 127 b of sub-speed control arm127 having been disposed at low-speed position 129 is rotated tohigh-speed position 130. Accordingly, link arm 177 is rotated centeredon control shaft 301 and pulls link rod 178 in a direction designated byan arrow 185. Accordingly, link arm 179 is rotated centered on pivotshaft 181 in a direction designated by an arrow 186 so that long linkportion 179 b pushes link rod 180 in a direction designated by an arrow198, thereby rotating drive-mode change operation arm 157 having beendisposed at four-wheel drive mode position 184 to two-wheel drive modeposition 183. Therefore, during high-speed traveling, vehicle 1 isautomatically driven by two wheels advantageously for efficient fuelconsumption.

As shown in FIG. 20, a rotation angle 187 of operation portion 127 b ofsup-speed control arm 127 between low-speed position 129 and high-speedposition 130 is smaller than a rotation angle 188 of drive-mode changeoperation arm 157 between four-wheel drive mode position 184 andtwo-wheel drive mode position 183. However, due to the difference oflength between short and long link portions 179 a and 179 b in link arm179, the small movement of link rod 178 pivoted on the tip of short linkportion 179 a is converted into the large movement of link rod 180pivoted on the tip of long link portion 179 b so as to correspond to thelarge rotation angle 188 of drive-mode change operation arm 157 betweenfour-wheel drive mode position 184 and two-wheel drive mode position183. In this way, linkage system 189 serves as a cushion mechanismcompensating for the difference of movement degree between sub-speedcontrol arm 172 and drive-mode change operation arm 157.

Due to linkage system 189 between sub-speed control arm 127 anddrive-mode change operation arm 157, the drive-mode change operation isautomatically performed according to the sub-speed change operationbetween the high-speed stage and the low-speed stage. When vehicle 1requires a large traction power for work or traveling on a rough road, adriver sets sub-speed control lever 174 to the low-speed position so asto determine the large displacement of hydraulic motor 19, andsimultaneously, the drive mode is automatically set to the four-wheeldrive mode. When vehicle 1 normally travels on a road, the driver setssub-speed control lever 174 to the high-speed position so as todetermine the small displacement of hydraulic motor 19, andsimultaneously, the drive mode is automatically set to the two-wheeldrive mode, thereby ensuring efficient fuel consumption.

Referring to FIG. 18, control shaft 301 serving as the pivot shaft ofsub-speed control arm 127 has a center axis (rotary axis) 163 inparallel to center axis (rotary axis) 162 of rotary valve shaft 158 ofdrive-mode change valve 135. Linkage system 189 is compactly interposedbetween sub-speed control arm 127 and drive-mode change operation arm157 having the small distance between center axes 162 and 163, therebyfore-and-aft minimizing rear hydrostatic transaxle 35.

Referring to FIG. 21, a sub-speed control linkage system betweensub-speed control arm 127 and sub-speed control lever 174 will bedescribed.

Although sub-speed control arm 127 of each of transaxles 3 and 35 isshiftable between two positions 129 and 130 as shown in FIGS. 8, 19 and20, the sub-speed control linkage system shown in FIG. 21 is configuredso as to shift sub-speed control lever 174 and sub-speed control arm 127among three positions. The sub-speed control linkage system can beeasily redesigned to be shiftable between two positions so as to beadapted to transaxle 3 or 35.

A bracket 190 is disposed beside driver's seat 7 in vehicle 1. Bracket190 is vertically reversed L-shaped when viewed in front so as to have ahorizontal top plate portion 190 a and a vertical plate portion 190 bextended downward top plate portion 190 a. A pivot shaft 193 projectslaterally from vertical plate portion 190 b of bracket 190. A link arm194 is pivoted on pivot shaft 193 rotatably in a direction designated byan arrow 196. Sub-speed control lever 174 is pivoted at its bottom endonto a top end of link arm 194 rotatably in a direction designated by anarrow 195 perpendicular to the direction designated by arrow 196.Connection rod 173 is pivotally interposed between a bottom end of linkarm 194 and the tip of operation portion 127 b of sub-speed control arm127.

A lever guide slot 191 is bored in top plate portion 190 a of bracket190, and sub-speed control lever 174 is passed through lever guide slot191, and extended upward from top plate portion 190 a so as to befixedly provided on its top end with a grip 174 a. A torsion spring 192is engaged at one end thereof onto a vertical intermediate portion ofsub-speed control lever 174 below top plate portion 190 a of bracket190, and is engaged at the other end thereof onto vertical plate portion190 b of bracket 190, so as to bias sub-speed control lever 174 towardvertical plate portion 190 b in the direction designated by arrow 195.Lever guide slot 191 is E-shaped when viewed in plan so as to include ashift slot 191 d extended in the fore-and-aft direction designated byarrow 196, and three parallel location slots, i.e., a low-speed positionslot 191 a, a middle-speed position slot 191 b and a high-seed positionslot 191 c, extended from shift slot 191 d in the lateral directiondesignated by arrow 195.

To operate for sub-speed change, a driver gripping grip 174 a rotatessub-speed control lever 174 in the direction designated by arrow 195, soas to insert sub-speed control lever 174 from one of location slots 191a, 191 b and 191 c into shift slot 191 d. Then, sub-speed control lever174 is rotated along shift slot 191 d in the direction designated byarrow 196, and rotated into target location slot 191 a, 191 b or 191 cin the direction designated by arrow 195. Due to the force of spring192, sub-speed control lever 174 finally abuts against an end of targetlocation slot 191 a, 191 b or 191 c, so as to be surely retained in thetarget location slot. Since the rotation sub-speed control lever 174 inthe direction designated by arrow 196 is centered on pivot shaft 193,operation portion 127 b of sub-speed control arm 127 connected tosub-speed control lever 174 through connection rod 173 is also rotatedin the direction designated by arrow 196, so as to be shifted among alow-speed position 197 a, a middle-speed position 197 b and a high-speedposition 197 c corresponding to respective low-speed position slot 191a, middle-speed position slot 191 b and high-speed position slot 191 c.

In this way, the sub-speed control linkage system shown in FIG. 21provides three sub-speed stages. To adapt the sub-speed control linkagesystem to sub-speed control arm 127 shiftable between two positions asshown in FIGS. 19 and 20, for instance, lever guide groove 191 isreshaped to have only two location slots. Even if sub-speed control arm127 is shifted among three or more speed stages, an alternative linkratio of linkage system 189 can be set, and valve port portion 158 a ofrotary valve shaft 158 of drive-mode change valve 135 can be formed inan alternative shape, so that the drive-mode change between thefour-wheel drive mode and the two-wheel drive mode corresponds to ashift between any two speed stages selected from the three or more speedstages.

Referring to FIG. 23, an alternative duct plate 199, an alternativemotor casing 200 incorporating hydraulic motor 19, and an alternativevalve casing 201 of drive-mode change valve 135, adapted in transaxle35, will be described. Similar to duct plate 154, an alternative ductplate 199 is fixed on the front surface of front casing part 96 (notshown), so that hydraulic pump 17 (not shown) is fitted onto a verticalupper rear surface of duct plate 199, and hydraulic motor 19 with outputshaft 155 is fitted onto a vertical lower front surface of duct plate199.

Motor casing 200 is fixed onto the front surface of duct plate 199 so asto incorporate hydraulic motor 19, and valve casing 201 of drive-modechange valve 135 is fixed onto a front surface of motor casing 200.Rotary valve shaft 158 having valve port portion 158 a with the pair ofvalve ports 135 d is rotatably inserted into valve casing 201, similarlyto that in drive-mode change valve casing 135 a.

Duct plate 199 is bored therein with fluid ducts corresponding torespective fluid ducts 144 and 141. A forwardly opened fluid duct 199 ais bored in duct plate 199 so as to correspond to a part of fluid duct144. The other structure of duct plate 199 than fluid duct 199 a issimilar to that of duct plate 154. In valve casing 201, fluid ductscorresponding to fluid ducts 135 e, 135 f, 135 g and 135 h are bored,and a rearwardly opened fluid duct 201 a is extended from the fluid ductcorresponding to fluid duct 135 e. In a side wall of motor casing 200, afore-and-aft penetrating fluid duct 200 a corresponding to fluid pipe145 is bored so as to be opened at its front end to fluid duct 201 a,and opened at its rear end to fluid duct 199 a. Similarly, a fluid ductcorresponding to fluid pipe 142 (not shown) is also bored in motorcasing 200 so as to be opened to the fluid duct in duct plate 199corresponding to fluid duct 141, and opened to the fluid duct in valvecasing 201 corresponding to fluid duct 135 f.

In this way, with respect to the embodiment shown in FIG. 23, the fluidsupply system for supplying fluid from the closed fluid circuit formedin duct plate 199 of HST 30 to drive-mode change valve 135 includes noexposed fluid pipe such as fluid pipes 145 and 142, thereby facilitatingfor assembling of transaxle 35.

Referring to FIGS. 24 to 26, an alternative linkage system 212 forlinking the drive-mode change operation to the sub-speed changeoperation will be described. In this regard, a sub-speed control armassembly 202 is provided on the distal end of control shaft 301projecting outward from side cover 126. Sub-speed control arm assembly202 includes an L-shaped restriction arm 203 fixed on control shaft 301,an operation arm 204 provided on control shaft 301 rotatably relative torestriction arm 203, and a spring 205 interposed between arms 203 and204. Connection rod 173 extended from sub-speed control lever 174 ispivoted at its end onto a tip portion of operation arm 204. A link rod206 is extended from drive-mode change operation arm 157, and is pivotedat its end onto an intermediate portion of operation arm 204. In thisway, linkage system 212 comprises: sub-speed control arm assembly 202including arms 203 and 204; drive-mode change operation arm 157; andlink rod 206 interposed between arms 204 and 157.

L-shaped restriction arm 203 includes: a boss 203 c fixed on controlshaft 301; a restriction portion 203 a extended forward from boss 203 c;and a connection portion 203 b extended upward from boss 203 cperpendicular to restriction portion 203 a. As mentioned above, U-shapedrestriction wall 126 a is formed on side cover 126 so as to have upperand lower wall portions 126 a 1 and 126 a 2, and restriction portion 203a is fitted into restriction wall 126 a between upper and lower wallportions 126 a 1 and 126 a 2. Operation arm 204 is formed at its bottomportion with a boss 204 a relatively rotatably fitted on boss 203 c ofrestriction arm 203. While operation arm 204 connected to sub-speedcontrol lever 174 and drive-mode change operation arm 157 is rotatablebetween low-speed position 129 corresponding to the low-speed positionof sub-speed control lever 174 and a lever's high-speed position 207corresponding to the high-speed position of sub-speed control lever 174,upper and lower wall portions 126 a 1 and 126 a 2 of restriction wall126 a restrict the rotatable range of connection portion 203 b ofrestriction arm 203 fixed on control shaft 301 between low-speedposition 129 corresponding to the low-speed (large displacement)position of motor swash plate 117 and motor's high-speed position 130,which is nearer to low-speed position 129 than lever's high-speedposition 207 and corresponds to the high-speed (small displacement)position of motor swash plate 117.

Spring 205 is wound around boss 204 c of operation arm 204. Both endportions of spring 205 are twisted to cross each other, and extended soas to pinch connection portion 203 b of restriction arm 203 andoperation arm 204.

Due to this configuration, when sub-speed control lever 174 having beendisposed at the low-speed position is operated to the high-speedposition, operation arm 204 connected to sub-speed control lever 174through connection rod 173 is rotated from low-speed position 129 tolever's high-speed position 207 in a direction designated by an arrow209, so as to rotate drive-mode change operation arm 157 connected tooperation arm 204 through link rod 206 from four-wheel drive modeposition 184 to two-wheel drive mode position 183 in a directiondesignated by an arrow 211.

Due to spring 205, connection portion 203 b of restriction arm 203 isrotated together with operation arm 204 from low-speed position 129 inthe direction designated by arrow 209. When connection portion 203 b ofrestriction arm 203 rotated from low-speed position 129 reaches motor'shigh-speed position 130 corresponding to the high-speed position ofmotor swash plate 117, restriction portion 203 a of restriction arm 203abuts at its bottom edge against an upper surface of lower wall portion126 a 2 of restriction wall 126 a, thereby stopping the rotation ofrestriction arm 203. However, sub-speed control lever 174 is stillrotated to its high-speed position so that operation arm 204 stillrotates according to the rotation of sub-speed control lever 174 againstspring 205 (in this state, operation arm 204 pushes one end portion ofspring 205 away from the other end portion of spring 205 retained byconnection portion 203 b of restriction arm 203). When operation arm 204reaches lever's high-speed position 207 corresponding to the high speedposition of sub-speed control lever 174, drive-mode change operation arm157 reaches two-wheel drive mode position 183.

On the contrary, when sub-speed control lever 174 having been disposedat the high-speed position is operated to the low-speed position,operation arm 204 is rotated from lever's high-speed position 207 tolow-speed position 129 through motor's high-speed position 130 in adirection designated by an arrow 208. During rotation of operation arm204 from lever's high-speed position 207 to motor's high-speed position130, restriction arm 203 is retained at motor's high-speed position 130by lower wall portion 126 a 2 of restriction wall 126 a. During rotationof operation arm 204 from motor's high-speed position 130 to low-speedposition 129, restriction arm 203 is rotated integrally with operationarm 204. When restriction portion 203 a of restriction arm 203 abuts atits upper edge against a lower surface of upper wall portion 126 a 1 ofrestriction wall 126 a, connection portion 203 b of restriction arm 203and operation arm 204 reach low-speed position 129. Due to the rotationof operation arm 204 from lever's high-speed position 207 to low-speedposition 129, drive-mode change operation arm 157 connected to operationarm 204 through link rod 206 is rotated from two-wheel drive modeposition 183 to four-wheel drive mode position 184.

In comparison with linkage system 189, linkage system 212 includes nocomponent, such as link arm 179 having short and long link portions 179a and 179 b, which must be formed to correspond to the difference oflink ratio between sub-speed control arm 127 and pivot shaft 181 fromthe link ratio between pivot shaft 181 and drive-mode change operationarm 157. Therefore, linkage system 212 can be easily configured withfewer components.

Additionally, drive-mode change operation arm 157 can be optionallyrotated for changing the drive-mode of vehicle 1, and the sub-speedstage can be automatically changed by the drive-mode changing operation.In this regard, when drive-mode change operation arm 157 is disposed atfour-wheel drive mode position 184, operation arm 204 connected todrive-mode change operation arm 157 through link rod 206 is retained atlow-speed position 129 so as to be disposed in parallel to drive-modechange operation arm 157 disposed at four-wheel drive mode position 184.In this state, spring 205 biases operation arm 204 and connectionportion 203 b of restriction arm 203 in the direction designated byarrow 208, so that restriction portion 203 a of restriction arm 203 ispressed against upper wall portion 126 a 1 of restriction wall 126 a soas to retain connection portion 203 b at low-speed position 129.

When drive-mode change operation arm 157 is manually rotated fromfour-wheel drive mode position 184 to two-wheel drive mode position 183in the direction designated by arrow 211, operation arm 204 connected todrive-mode change operation arm 157 through link rod 206 is rotated fromlow-speed position 129 to lever's high-speed position 207 in thedirection designated by arrow 209. During the rotation of operation arm204 from low-speed position 175 to motor's high-speed position 130,restriction arm 203 is rotated integrally with operation arm 204 byspring 205 so as to shift motor swash plate 117 from the low-speed(large displacement) position to the high-speed (small displacement)position. While operation arm 204 rotates from motor's high-speedposition 130 to lever's high-speed position 207 against spring 205,connection portion 203 b of restriction arm 203 is retained at motor'shigh-speed position 130 by pressing restriction portion 203 a ofrestriction arm 203 against lower wall portion 126 a 2 of restrictionwall 126 a.

When drive-mode change operation arm 157 is rotated from two-wheel drivemode position 183 to four-wheel drive mode position 184, motor swashplate 117 is retained at the high-speed (small displacement) positionduring the rotation of operation arm 204 from lever's high-speedposition 207 to motor's high-speed position 130, and motor swash plate117 is shifted from the high-speed (small displacement) position to thelow-speed (large displacement) position by the rotation of restrictionarm 203 together with operation arm 204 from motor's high-speed position130 to low-speed position 129.

In this way, linkage system 212 links the drive-mode change operation tothe sub-speed change operation, and links the sub-speed change operationto the drive-mode change operation. In linkage system 212, spring 205functions as a cushion mechanism which allows the rotation of operationarm 204 for rotating drive-mode change operation arm 157 to two-wheeldrive mode position 183 while restriction arm 203 is retained forretaining motor swash plate 117 at its high-speed (small displacement)position.

Referring to FIGS. 27 to 42, four embodiments of auxiliary pumps forsupplying fluid to hydraulically driven devices, adaptable to eithertransaxle 3 or 35, will be described. Referring to one embodiment shownin FIG. 27 and 28, an auxiliary pump casing 213 a incorporating acircumscribed gear pump serving as an auxiliary pump 213 is fitted ontoa front surface of an alternative charge pump casing 76 incorporatingcharge pump 15, and fastened together with charge pump casing 176 toduct plate 154 (this is representative. It may be duct plate 48 or 199)by bolts 231. A pump drive shaft 227 drivingly connected to engine 14 iscoaxially and rotatably integrally connected to input shaft 16 through asleeve 232 journalled between casings 176 and 213 a through a bearing.In this way, charge pump 15 and auxiliary pump 213 are aligned coaxiallyto input shaft 16.

Auxiliary pump 213 includes mutually meshing gears 228 and 230 disposedin auxiliary pump casing 213 a. Gear 228 is formed on pump drive shaft227, and gear 230 is formed on a pump driven shaft 229 disposed inparallel to pump drive shaft 227. By transmitting the engine power topump drive shaft 227 and input shaft 16, charge pump 15 is driven so asto suck fluid from traveling gear chamber 72 b in transaxle 3 or 35through filter 90, and simultaneously, auxiliary pump 213 is driven soas to suck fluid extracted through port 94 from fluid flowing towardcharge pump 15. Gears 228 and 230 of auxiliary pump 213 rotate todeliver the fluid into an outwardly opened delivery port 235 provided onauxiliary pump casing 213 a.

In this embodiment, vehicle 1 is equipped with a front loader, and witha damping cylinder and a lifting cylinder serving as hydraulic actuatorsfor the front loader. A delivery fluid pipe 219 is extended fromdelivery port 235 and fluidly connected to changeover valves 214 and 215in a valve unit for the front loader. Changeover valve 214 is fluidlyconnected to the damping cylinder through ports 223 and 224 so as tocontrol a damping action of a bucket of the front loader. Changeovervalve 215 is fluidly connected to the lifting cylinder through ports 225and 226 so as to raise and lower the front loader. A returning fluidpassage 221 is disposed in the valve unit for the front loader, and areturning fluid pipe 222 is extended from the valve unit, and isinterposed between fluid passage 221 and port 95 provided on duct plate154, so as to return fluid to traveling gear chamber 72 b through port95.

As shown in FIGS. 27, when changeover valves 214 and 215 are disposed attheir neutral positions so as to stop the damping cylinder and liftingcylinder for the front loader, the fluid from delivery port 235 andfluid pipe 219 is passed through changeover valves 214 and 215, and issupplied through a fluid passage 220 to a changeover valve 216 forhydraulic lift cylinder 11 for rotating lift arms 218 to be connected toa rear-mount working machine disposed behind vehicle 1. The fluiddrained from changeover valve 216 is joined to fluid passage 222 so asto be returned to traveling gear chamber 72 b through port 95.

In this way, auxiliary pump 213 sufficiently supplies fluid for drivingthe front loader and lift arms 218 while charge pump 15 supplies fluidto HST 20 or 30, main PTO clutch 37 and power steering cylinder 70.

FIGS. 29 and 30 illustrate an alternative auxiliary dual pump unit 236.In pump unit 236, a second auxiliary pump casing 248 incorporating asecond auxiliary pump 236 b is fixed onto a front surface of a firstauxiliary pump casing 247 incorporating a first auxiliary pump 236 a.Pump unit 236 includes a stay 250 fixed on first auxiliary pump casing247 so as to be fastened to an outer surface of engine 14 or transaxlecasing 3 or 35.

Mutually joined pump casings 247 and 248 incorporate a pump drive shaft240, on which a drive gear 241 is formed or fixed in first auxiliarypump casing 247, and on which a drive gear 242 is formed or fixed insecond auxiliary pump casing 248. In first auxiliary pump casing 247, apump driven shaft 243 is supported in parallel to pump drive shaft 240,and is formed or fixed thereon with a driven gear 244 meshing with drivegear 241 so as to constitute first auxiliary pump 236 a. In secondauxiliary pump casing 248, a pump driven shaft 245 is supported inparallel to pump drive shaft 240, and is formed or fixed thereon with adriven gear 246 meshing with drive gear 242 so as to constitute secondauxiliary pump 236 b.

A pulley 239 is fixed on a rear end of pump drive shaft 240, a pulley237 is fixed on pump drive shaft 227 interposed between engine 14 andinput shaft 16, and a belt 238 is interposed between pulleys 237 and 239so as to transmit the engine power to pump drive shaft 240, therebydriving first and second auxiliary pumps 236 a and 236 b.

By transmitting the engine power to pump drive shaft 227 and input shaft16, charge pump 15 is driven so as to suck fluid from traveling gearchamber 72 b in transaxle 3 or 35 through filter 90, and simultaneously,first and second auxiliary pumps 236 a and 236 b are driven so as tosuck fluid extracted through port 94 from fluid flowing toward chargepump 15.

Fluid delivered from first auxiliary pump 236 a is joined to the fluiddelivered from charge pump 15, so as to be sufficiently supplied to mainPTO clutch 37 and power steering cylinder 70. Similar to the fluiddelivered from auxiliary pump 213, fluid delivered from second auxiliarypump 236 b is supplied to the valve unit for the front loader includingchangeover valves 214 and 215, then it is supplied to hydraulic liftcylinder 11 for rotating lift arms 218, and it is returned to travelinggear chamber 72 b through port 95. Due to auxiliary pump unit 236,charge pump 15 can sufficiently supply fluid to the closed fluid circuitof HST 20 or 30.

Referring to FIGS. 31 to 39, an alternative auxiliary pump unit 400 forsupplying fluid to hydraulic lift cylinder 11 for rotating lift arms 218is provided on a front end of transaxle 3 or 35 so as to be offset frominput shaft 16. With respect to the present embodiment, auxiliary pumpunit 400 provided on transaxle 3 including mechanical drive-mode changeclutch 29 is illustrated, however, auxiliary pump unit 400 can beprovided on the front end of transaxle 35 incorporating drive-modechange valve 135.

In this embodiment, an alternative charge pump casing 276 of charge pump15 is fixed on a front surface of an alternative duct plate 348,auxiliary pump unit 400 is mounted on a front surface of charge pumpcasing 276, hydraulic pump 17 is fitted onto a rear surface of ductplate 348, hydraulic motor 19 is fitted onto the front surface of ductplate 348, and motor casing 26 is fixed onto duct plate 348 so as toincorporate hydraulic motor 19, thereby constituting a front unit 31 asshown in FIGS. 34 to 36. To constitute front unit 31 for transaxle 3,clutch casing 27 incorporating drive-mode change clutch 29 is fixed onthe front surface of motor casing 27, as illustrated. Alternatively, toconstitute front unit 31 for transaxle 35, drive-mode change valve 135is fixed on the front surface of motor casing 27. Duct plate 348 offront unit 31 is fixed onto the front surface of front casing part 96,thereby completing transaxle 3 or 35.

As shown in FIG. 32, duct plate 348 is bored therein with a fore-and-aftpenetrating fluid duct 348 a. Fluid duct 348 a is opened at its rear endto port 96 e formed in front casing part 96, so as to receive fluid fromtraveling gear chamber 72 b in front casing part 96 through fluid duct92, and opened at its front end to a rear end opening of a fore-and-aftfluid duct 276 b formed in charge pump casing 276.

As shown in FIGS. 32 and 38, in charge pump casing 276, a fluid duct 276b is connected to a lateral intermediate portion of a laterally extendedsuction fluid gallery 276 c. Suction fluid gallery 276 c is connected atits left end to a suction port 276 d. Suction port 276 d is opened to apump chamber 276 a incorporating inner and outer rotors 15 a and 15 b ofcharge pump 15. In this way, fluid is supplied from traveling gearchamber 72 b to pump chamber 276 a.

A delivery port 276 e is also opened to pump chamber 276 a. Duct plate348 is provided therein with relief valve 40 and the pair of chargecheck valves 43F and 43R (with orifice 44), and as shown in FIG. 38,charge pump casing 276 is provided therein with port 68, resistancevalve 41 and reducing valve 42, similar to those in duct plate 48 andcharge pump casing 76 as mentioned above. The fluid delivered fromcharge pump 15 into delivery port 276 e is supplied to HST 20 or 30through relief valve 40, reducing valve 42 and charge check valve 43F or43R, and a part of the fluid is supplied to power steering cylinder 70through resistance valve 41 and changeover valve 67. A fluid duct 276 uis bored in charge pump casing 276 so as to serve as a delivery fluidduct from charge pump 15 to reducing valve 42, and fluid duct 73 isbored in charge pump casing 276 so as to supply fluid from reducingvalve 42 to charge check valves 43F and 43R. The fluid drained frompower steering cylinder 70 is introduced into port 69 formed on a leftside surface of charge pump casing 276 as shown in FIG. 35, and returnedto pump chamber 72 a through a fore-and-aft fluid duct 276 t formed incharge pump casing 276. Further, the fluid released from reducing valve42 is supplied to PTO clutch control valve 39. In detail, the fluiddelivered from charge pump 15 is supplied on the route as mentionedabove.

Auxiliary pump unit 400 includes: a gear cover 401 fixed on a frontsurface of charge pump casing 276; a connection block 402 fixed on afront surface of gear cover 401; an auxiliary pump casing 403 fixed on afront surface of connection block 402; and auxiliary pump 420 disposedin auxiliary pump casing 403. Mutually joined connection block 402 andauxiliary pump casing 403 are offset laterally (rightward) from inputshaft 16 projecting forward from gear cover 401.

A forward opened recess 276 f is formed in charge pump casing 276, andcovered at its front opening with the rear surface of gear cover 401 soas to serve as a gear chamber 410, which incorporates gears 411, 412 and413 serving as a gear train for transmitting the rotary force of inputshaft 16 to auxiliary pump 420 disposed in auxiliary pump casing 403.Gear 411 is fixed on input shaft 16 through a pair of opposite radialretaining pins 411 a as shown in FIG. 35. A counter gear shaft 412 a isdisposed in parallel to input shaft 16, and supported at its front endby gear cover 401, and at its rear end by charge pump casing 276. Gear412 is provided on counter gear shaft 412 a in gear chamber 410 andmeshes with gear 411. Gear 413 is journalled by charge pump casing 276and gear cover 401 through respective bearings, and meshes with gear412.

In auxiliary pump casing 403, auxiliary pump 420 includes mutuallycircumscribed-meshing drive and driven gears 422 and 424. Drive gear 422is formed or fixed on a pump drive shaft 423, and driven gear 424 isformed or fixed on a pump driven shaft 425. Shafts 423 and 425 aredisposed in parallel to each other and in parallel to input shaft 16 andcounter gear shaft 412 a, and are rotatably supported at their frontends by auxiliary pump casing 403, and at their rear portions byconnection block 402. Pump drive shaft 423 is extended rearward fromconnection block 402, and rotatably integrally spline-fitted into aforwardly extended boss of gear 413 in gear cover 401. In this way,gears 422 and 424 of auxiliary pump 420 are driven by the rotary forceof input shaft 16 through gears 411, 412 and 413.

Auxiliary pump 420 receives a part of fluid supplied to charge pump 15,and supplies fluid to changeover valve 216 for controlling hydrauliclift cylinder 11 for rotating lift arms 218. In this regard, charge pumpcasing 276 is formed therein with laterally extended suction fluidgallery 276 c connected at its left end to suction port 276 d of chargepump 15, as shown in FIG. 38, and is formed in its rightward expandedportion with a fore-and-aft penetrating fluid duct 276 g connected atits front end to a right end of suction fluid duct 276 c, as shown inFIG. 39. Namely, suction fluid gallery 276 c distributes fluid thereinbetween charge pump 15 and auxiliary pump 420.

As shown in FIG. 39, the front opening of fluid duct 276 g is formed asa port 430, into which a fore-and-aft horizontal fluid pipe 431 isfitted at its rear end. Auxiliary pump casing 403 is provided thereinwith a vertical fluid duct 403 a. Fluid pipe 431 is fitted at its frontend into charge pump casing 403, and is connected to a bottom portion offluid duct 403 a. Fluid duct 403 a is connected at its top end to asuction port of auxiliary pump 420 just below gears 422 and 424.

In auxiliary pump casing 403, a vertical delivery fluid duct 403 b isbored and extended upward from a delivery port of auxiliary pump 420just above gears 422 and 424. As shown in FIG. 34, a port 432 isprovided onto a top of charge pump casing 403, and is connected to thetop of delivery fluid duct 403 b. A fluid pipe 433 is extended from port432, and is connected to changeover valve 216 for hydraulic liftcylinder 11 for rotating lift arms 218.

Changeover valve 216 is fixedly mounted on a horizontal top surface 276h of charge pump casing 276, as shown in FIG. 36. As shown in FIGS. 35and 39, a forwardly opened recess 276 j is formed in charge pump casing276 along the upper edge of gear chamber 410, and covered with the rearsurface of gear cover 401 so as to serve as a drain fluid gallery 415. Avertical fluid duct 276 i is extended upward from a right end of drainfluid gallery 415, so that fluid from a tank port 216 a of changeovervalve 216 falls through fluid duct 236 i into drain fluid gallery 166.Drain fluid gallery 415 is connected to gear chamber 410 through aconnection duct 276 k facing gear 413 on pump drive shaft 423. Gearchamber 410 is configured so that gear 413 is disposed slightly higherthan gears 412 and 411. Therefore, the fluid collected in drain fluidgallery 415 is gradually dropped through connection duct 276 k onto gear413 in gear chamber 410, so as to lubricate all gears 413, 412 and 411in gear chamber 410. Incidentally, drain fluid gallery 415 may beconnected at its left end portion to port 69 so as to collect fluid frompower steering cylinder 70.

As shown in FIGS. 35 and 37, a rearwardly opened recess 276 m is formedin charge pump casing 276, and covered with the front surface of ductplate 348 so as to serve as a fluid gallery 416. A fluid duct 276 p isextended from resistance valve 41 (not shown) disposed in charge pumpcasing 276, and is opened to an upper end portion of fluid gallery 416.A fluid duct 276 q is extended from a laterally middle upper portion ofgear chamber 410, and is opened to a lower end portion of fluid gallery416. In this way, fluid leaked from a spring chamber of resistance valve41 is drained into gear chamber 410 through fluid duct 276 p, fluidgallery 416 and fluid duct 276 q, so as to be prevented from beingapplied onto resistance valve 41 as a hydraulic backpressure.

As shown in FIGS. 31 and 35, a laterally extended fluid hole 276 r isopened at a bottom portion of gear chamber 410 between gears 411 and412. In charge pump casing 276, a fluid duct 276 s is extended from hole276 r and opened rearward. A rearwardly and downwardly slanted fluidduct 348 b and a horizontal fluid duct 348 c are bored in duct plate348. Fluid duct 348 b is connected at its upper front end to fluid duct276 s in charge pump casing 276, and at its lower rear end to fluid duct348 c. Fluid duct 348 c fore-and-aft penetrates duct plate 348, so as tobe opened at its front end to a fluid sump in motor casing 26 (or 200),and at its rear end to the fluid sump in traveling gear chamber 72 b infront casing part 96. In this way, fluid is smoothly drained from gearchamber 410 into motor casing 26 (or 200) and traveling gear chamber 72b , whereby gears 411, 412 and 413 are prevented from agitatingresistant fluid collected at the bottom portion of gear chamber 410,thereby reducing power loss. In this regard, the opening area of fluidduct 276 k to gear chamber 410 is determined so as to optimally restrictfluid dropped from drain fluid gallery 415 into gear chamber 410.

Referring to FIGS. 40 to 42, an auxiliary pump unit 500 is mounted on arear end of hydrostatic transaxle 35 having drive-mode change valve 132.Auxiliary unit 500 may be mounted on a rear end of hydrostatic transaxle3 having drive-mode change clutch 29. The main casing of transaxle 3 or35 and some parts and components therein shown in FIG. 40 are strictlydifferent in shape, direction and location from those shown in FIGS. 2and 13 because main PTO clutch 37 is not disposed coaxially to inputshaft 16. However, in this embodiment, the components and parts aredesignated by the same reference numerals in the above embodiments ifthey have the same functions as those of the above embodiments.

In auxiliary pump unit 500, an auxiliary pump casing 501 is fixed on anupper rear end surface of rear casing part 97 so as to project rearward.Auxiliary pump casing 501 incorporates mutually circumscribed-meshingdrive and driven gears 511 and 512 serving as an auxiliary pump 510. Inauxiliary pump casing 501, a pump drive shaft 502 and a pump drive shaft503 are disposed in parallel to each other and rotatably supported.Drive gear 511 is fixed on pump drive shaft 502, and driven gear 512 isfixed on pump driven shaft 503. Auxiliary pump casing 501 is covered atits rear end with a cover 501 a. In front casing part 96, input shaft 16is rotatably integrally connected to coaxial pump drive shaft 502through a gear 504 just behind vertical partition wall 96 b between pumpchamber 72 a and traveling gear chamber 72 b (in traveling gear chamber72 b ).

In this way, auxiliary pump 510 is driven by rotation of input shaft 16so as to supply fluid to lift cylinder 11 for rotating the pair of leftand right lift arms 218 pivoted on the top of front casing part 96through a bracket 520. The pair of left and right lift arms 218 arerotatably integrally connected to each other through a lateralconnection shaft 218 a spanned in bracket 520. A piston rod of liftcylinder 11 is connected to connection shaft 218 so as to verticallyrotate lift arms 218 with connection shaft 218 a by its telescopicmovement.

A fore-and-aft extended PTO clutch drive shaft 505 is disposed inparallel to input shaft 16 and pump drive shaft 502. A gear 506 is fixedon PTO clutch drive shaft 505 just behind partition wall 96 b, andmeshes with gear 504. PTO clutch drive shaft 505 is journalled bypartition wall 96 b through a bearing. A pump chamber bottom wall 96 iis extended forward from the bottom end of partition wall 96 b, and asupport wall 96 j projects upward from pump chamber bottom wall 96 ijust behind duct plate 154. PTO clutch drive shaft 505 is extendedforward along pump chamber bottom wall 96 i in pump chamber 72 a, and isjournalled at its front end by support wall 96 j through a needlebearing.

PTO clutch drive shaft 505 is extended rearward from gear 506 andrelatively rotatably fitted at its rear end into coaxial PTO clutchdriven shaft 32. Main PTO clutch 37 is interposed between PTO clutchdrive shaft 505 and PTO clutch driven shaft 32. Description of main PTOclutch 37 shown in FIG. 40 is omitted because it is the same as thatshown in FIG. 2 if PTO clutch drive shaft 505 is regarded as input shaft16. Also, the drive train from main PTO clutch 37 to mid and rear PTOshafts 9 and 13 through sub PTO clutch 112 is similar to that mentionedabove.

Alternatively, PTO clutch drive shaft 505 may be supported as shown inFIG. 43. In this regard, a center boss portion 506 a of gear 506 isextended rearward along PTO clutch drive shaft 505 and inserted intorotary drum 36 of main PRO clutch 37. The clutch friction disks areinterposed between rotary drum 36 and center boss portion 506 a of gear506. Front and rear needle bearings 507 are interposed between PTOclutch drive shaft 505 and gear 506 extended along PTO clutch driveshaft 505, so as to stably journal PTO clutch drive shaft 505 just infront of main PTO clutch 37. Further, the front end of PTO clutch driveshaft 505 is simply fitted slidably rotatably into a shaft hole insupport wall 96 j.

It further understood by those skilled in the art that the foregoingdescription is a preferred embodiment of the disclosed apparatus andthat various changes and modifications may be made in the inventionwithout departing from the scope thereof claimed as follows.

1. A hydrostatic transaxle for a vehicle having a first axle and asecond axle, the hydrostatic transaxle comprising: a hydraulic pump; afirst hydraulic motor drivingly connected to the first axle; a closedcircuit fluidly connecting the hydraulic pump to the first hydraulicmotor; and a fluid-supply switching device shifted between a supplyposition for supplying fluid from the closed fluid circuit to a secondhydraulic motor, which is disposed on the outside of the hydraulictransaxle and is drivingly connected to the second axle, and asupply-stop position for stopping the supply of fluid from the closedfluid circuit to the second hydraulic motor.
 2. The hydrostatictransaxle according to claim 1, the first hydraulic motor being variablein displacement, further comprising: a linkage system for associatingthe switching of the fluid-supply switching device between the supplyposition and the supply-stop position with operation for changing thedisplacement of the first hydraulic motor.
 3. The hydrostatic transaxleaccording to claim 2, wherein the first hydraulic motor is provide witha rotary shaft for changing the displacement of the first hydraulicmotor, and wherein the fluid-supply switching device is a rotary valvehaving a rotary axis disposed in parallel to the rotary shaft of thefirst hydraulic motor.
 4. The hydrostatic transaxle according to claim2, further comprising: a displacement control device for changing thedisplacement of the first hydraulic motor, the displacement controldevice having a movable range between at least two positions; and acushion mechanism provided in the linkage system so as to make the twopositions of the displacement control device in the movable rangecorrespond to the supply and supply-stop positions of the fluid-supplyswitching device, respectively, even when the movable range of thedisplacement control device is different from the shiftable range of thefluid-supply switching device between the supply position and thesupply-stop position.
 5. The hydrostatic transaxle according to claim 4,the linkage mechanism including: a link element interposed between thedisplacement control device and the fluid-supply switching device so asto serve as the cushion mechanism, wherein a link ratio between thedisplacement control device and the link element is different from alink ratio between the fluid-supply switching device and the linkelement so as to correspond to the difference of the movable range ofthe displacement control device and the shiftable range of thefluid-supply switching device.
 6. The hydrostatic transaxle according toclaim 4, the linkage mechanism including: an elastic element serving asthe cushion mechanism interposed between the displacement control deviceand the fluid-supply switching device so as to allow movement of one ofthe displacement control device and the fluid-supply switching devicewhile retaining the other of the displacement control device and thefluid-supply switching device.
 7. The hydrostatic transaxle according toclaim 2, wherein at least either a small displacement or a largedisplacement of the first hydraulic motor is selected, wherein thelinkage system sets the fluid-supply switching device to the supplyposition when the large displacement of the first hydraulic motor isselected, and wherein the linkage system sets the fluid-supply switchingdevice to the supply-stop position when the small displacement of thefirst hydraulic motor is selected.
 8. The hydrostatic transaxleaccording to claim 7, wherein the first hydraulic motor is provide witha rotary shaft for changing the displacement of the first hydraulicmotor, and wherein the fluid-supply switching device is a rotary valvehaving a rotary axis is disposed in parallel to the rotary shaft of thefirst hydraulic motor.
 9. The hydrostatic transaxle according to claim7, further comprising: a displacement control device for changing thedisplacement of the first hydraulic motor, the displacement controldevice having a movable range between a large displacement position forestablishing the large displacement of the first hydraulic motor and asmall displacement position for establishing the small displacement ofthe first hydraulic motor; and a cushion mechanism provided in thelinkage system so as to make the large displacement position of thedisplacement control device correspond to the supply position of thefluid-supply switching device, and to make the small displacementposition of the displacement control device correspond to thesupply-stop position of the fluid-supply switching device, even when themovable range of the displacement control device between the largedisplacement position and the small displacement position is differentfrom the shiftable range of the fluid-supply switching device betweenthe supply position and the supply-stop position.
 10. The hydrostatictransaxle according to claim 9, the linkage mechanism including: a linkelement interposed between the displacement control device and thefluid-supply switching device so as to serve as the cushion mechanism,wherein a link ratio between the displacement control device and thelink element is different from a link ratio between the fluid-supplyswitching device and the link element so as to correspond to thedifference of the movable range of the displacement control device andthe shiftable range of the fluid-supply switching device.
 11. Thehydrostatic transaxle according to claim 9, the linkage mechanismincluding: an elastic element serving as the cushion mechanisminterposed between the displacement control device and the fluid-supplyswitching device so as to allow movement of one of the displacementcontrol device and the fluid-supply switching device while retaining theother of the displacement control device and the fluid-supply switchingdevice.